How to

WCF + NHibernate: Entity Serialization

awgneo — Sat, 28 Jan 2012 22:29:15 GMT

Current revision posted to How to by awgneo on 28/01/2012 07:29:15 p.m.

WCF + NHibernate: Entity Serialization

Filed under: lazy loading, Nhibernate, FluentNH

I found many examples online covering how to serialize NHibernate entities for use over a WCF channel, while still using lazy and eager loading. In my application, my database models and my SOA models needed to be exactly the same; therefore, I wanted to avoid the use of DTOs. However, none of the examples I found quite worked for me.

Examples I found included:

IDataContractSurrogate (http://www.timvasil.com/blog14/post/2008/02/WCF-serialization-with-NHibernate.aspx) that allows WCF to attempt serialization by walking over the object graph (has a bug that does not allow proper XML generation: http://connect.microsoft.com/wcf/feedback/details/404241/method-object-getobjecttoserialize-object-obj-type-targettype-of-idatacontractsurrogate-can-not-return-null)
Standard Object Graph Walking (http://trentacular.com/2009/08/how-to-use-nhibernate-lazy-initializing-proxies-with-web-services-or-wcf/) this example did not work for me at all, but it was close to my final solution. Additionally, this example does not support collections.

My custom object graph walker (I hacked this out of some integrated code so it may need some tweaking):

using System;
using System.Collections.Generic;
using System.Collections;
using System.Reflection;
using System.Data;
using System.Linq;
using System.Configuration;
using FluentNHibernate.Cfg;
using FluentNHibernate.Cfg.Db;
using NHibernate;
using NHibernate.Cfg;
using NHibernate.Tool.hbm2ddl;
using FluentNHibernate.Automapping;
using Radiant.RQS.Services.Types;
using Radiant.RQS.Services.Core.Conventions;
using Radiant.RQS.Superbank;
using NHibernate.Proxy;
using NHibernate.Collection;
using NHibernate.Metadata;
using NHibernate.Type;
 
namespace Radiant.RQS.Services.Core
{
    public static class Resolver
    {
        public static List<T> ResolveList<T>(List<T> entityList, ISession session) where T : class
        {
            // create a resolved entities list for peace and sharing
            List<Object> resolvedEntities = new List<Object>();
            // loop over elements
            for (int entityListIndex = 0; entityListIndex < entityList.Count; entityListIndex++)
                entityList[entityListIndex] = Resolve<T>(entityList[entityListIndex], resolvedEntities, session);
 
<T>(entityList[entityListIndex], session, resolvedEntities);
 
            // done
            return entityList;
        }
 
        public static T[] ResolveArray<T>(T[] entityArray, ISession session) where T : class
        {
            // create a resolved entities list for peace and sharing
            List<Object> resolvedEntities = new List<Object>();
            // loop over elements
            for (int entityArrayIndex = 0; entityArrayIndex < entityArray.Length; entityArrayIndex++)
                entityArray[entityArrayIndex] = Resolve<T>(entityArray[entityArrayIndex], resolvedEntities, session);
 
<T>(entityArray[entityArrayIndex], session, resolvedEntities);
 
            // done
            return entityArray;
        }
 
        public static T Resolve<T>(T entity, ISession session) where T : class
        {
            // forward to resolver
            return Resolve<T>(entity, new List<Object>(), session);
<T>(entity, session, new List<Object>());
        }
 
        private static T Resolve<T>(T entity, List<Object> resolvedEntities, ISession session) where T : class
<T>(T entity, ISession session, List<Object> resolvedEntities) where T : class

        {
            // CHECKS //
 
            // if the entity is null, just skip it
            if (entity == null)
                return default(T);
            // if we have already resolved it, return that
            if (resolvedEntities.Contains(entity))
                return entity;
 
            // RESOLVE ENTITY //
 
            T resolvedEntity = default(T);
            // now lets go ahead and make sure everything is unproxied
            try { resolvedEntity = (T)session.GetSessionImplementation().PersistenceContext.Unproxy(entity); }
            catch (Exception ex) { return default(T); }
            // add entity to the list of resolved entities
            resolvedEntities.Add(resolvedEntity);
 
            // GET TYPE INFO //
 
            IClassMetadata entityMetadata = null;
            // get the entity type
            Type entityType = entity.GetType();
            // get the entity meta data from the type
            try { entityMetadata = session.SessionFactory.GetClassMetadata(entityType); }
            catch (Exception ex) { return default(T); }
 
            // PERFORM PROPERTY DIVE //
 
            String propertyName;
            Object propertyValue;
            Type propertyListType;
            IType entityPropertyType = null;
            Type propertyListInternalType;
            // get properties for this object
            PropertyInfo[] propertyInfos = entityType.GetProperties();
            // loop over source properties & compare
            foreach (PropertyInfo propertyInfo in propertyInfos)
            {
                // get property name
                propertyName = propertyInfo.Name;
                // get property type
                try { entityPropertyType = entityMetadata.GetPropertyType(propertyName); }
                catch (Exception ex) { continue; }
                // get property value
                propertyValue = propertyInfo.GetValue(entity, null);
                // these are not the good kind of bags :P
                if (entityPropertyType.IsCollectionType)
                {
                    // first get the property list's internal type
                    propertyListInternalType = propertyInfo.PropertyType.GetGenericArguments()[0];
                    // create new array type based on the internal type
                    propertyListType = typeof(List<>).MakeGenericType(propertyListInternalType);
                    // create a new property list of the internal type
                    IList propertyList = (IList)Activator.CreateInstance(propertyListType);
                    // set the property list in the resolved object
                    propertyInfo.SetValue(resolvedEntity, propertyList, null);
                    // get the enumerator for this property value
                    IEnumerator enumerator = ((IEnumerable)propertyValue).GetEnumerator();
                    // loop over items to also perform resolution
                    while (enumerator.MoveNext())
                        propertyList.Add(Resolve(enumerator.Current, session, resolvedEntities));
                }
                // destroy hibernate proxies
                else if (entityPropertyType.IsEntityType)
                {
                    // set the property of the resolved entity to the child beneath us
                    propertyInfo.SetValue(resolvedEntity, Resolve(propertyValue, session, resolvedEntities), null);
                }
            }
 
            // return the resolved entity :)
            return resolvedEntity;
        }
    }
}

This works FLAWLESSLY for me. When I lazy load or eager load sub-entities before calling Resolve() it perfectly serializes only what I want and does not attempt to lazy load the entire DB.

Example:

// get the computer query

var computerQuery =

from c in context.Session.Query<Types.Computer>()

where c.ID == computerID

select c;

// return computer

return Resolver.Resolve<Types.Computer>(computerQuery.SingleOrDefault(), session);

Let me know if this doesn't work for you :).

Thanks,
Alex G. (awgneo@xbetanet.com)

WCF + NHibernate: Entity Serialization

awgneo — Sat, 28 Jan 2012 22:23:22 GMT

Revision 4 posted to How to by awgneo on 28/01/2012 07:23:22 p.m.

WCF + NHibernate: Entity Serialization

Filed under: lazy loading, Nhibernate, FluentNH

Examples I found included:

IDataContractSurrogate (http://www.timvasil.com/blog14/post/2008/02/WCF-serialization-with-NHibernate.aspx) that allows WCF to attempt serialization by walking over the object graph (has a bug that does not allow proper XML generation: http://connect.microsoft.com/wcf/feedback/details/404241/method-object-getobjecttoserialize-object-obj-type-targettype-of-idatacontractsurrogate-can-not-return-null)
Standard Object Graph Walking (http://trentacular.com/2009/08/how-to-use-nhibernate-lazy-initializing-proxies-with-web-services-or-wcf/) this example did not work for me at all, but it was close to my final solution. Additionally, this example does not support collections.

My custom object graph walker (I hacked this out of some integrated code so it may need some tweaking):

using System;
using System.Collections.Generic;
using System.Collections;
using System.Reflection;
using System.Data;
using System.Linq;
using System.Configuration;
using FluentNHibernate.Cfg;
using FluentNHibernate.Cfg.Db;
using NHibernate;
using NHibernate.Cfg;
using NHibernate.Tool.hbm2ddl;
using FluentNHibernate.Automapping;
using Radiant.RQS.Services.Types;
using Radiant.RQS.Services.Core.Conventions;
using Radiant.RQS.Superbank;
using NHibernate.Proxy;
using NHibernate.Collection;
using NHibernate.Metadata;
using NHibernate.Type;
 
namespace Radiant.RQS.Services.Core
{
    public static class Resolver
    {
        public static List<T> ResolveList<T>(List<T> entityList, ISession session) where T : class
        {
            // create a resolved entities list for peace and sharing
            List<Object> resolvedEntities = new List<Object>();
            // loop over elements
            for (int entityListIndex = 0; entityListIndex < entityList.Count; entityListIndex++)
                entityList[entityListIndex] = Resolve<T>(entityList[entityListIndex], resolvedEntities, session);
 
            // done
            return entityList;
        }
 
        public static T[] ResolveArray<T>(T[] entityArray, ISession session) where T : class
        {
            // create a resolved entities list for peace and sharing
            List<Object> resolvedEntities = new List<Object>();
            // loop over elements
            for (int entityArrayIndex = 0; entityArrayIndex < entityArray.Length; entityArrayIndex++)
                entityArray[entityArrayIndex] = Resolve<T>(entityArray[entityArrayIndex], resolvedEntities, session);
 
            // done
            return entityArray;
        }
 
        public static T Resolve<T>(T entity, ISession session) where T : class
        {
            // forward to resolver
            return Resolve<T>(entity, new List<Object>(), session);
        }
 
        private static T Resolve<T>(T entity, List<Object> resolvedEntities, ISession session) where T : class
        {
            // CHECKS //
 
            // if the entity is null, just skip it
            if (entity == null)
                return default(T);
            // if we have already resolved it, return that
            if (resolvedEntities.Contains(entity))
                return entity;
 
            // RESOLVE ENTITY //
 
            T resolvedEntity = default(T);
            // now lets go ahead and make sure everything is unproxied
            try { resolvedEntity = (T)session.GetSessionImplementation().PersistenceContext.Unproxy(entity); }
            catch (Exception ex) { return default(T); }
            // add entity to the list of resolved entities
            resolvedEntities.Add(resolvedEntity);
 
            // GET TYPE INFO //
 
            IClassMetadata entityMetadata = null;
            // get the entity type
            Type entityType = entity.GetType();
            // get the entity meta data from the type
            try { entityMetadata = session.SessionFactory.GetClassMetadata(entityType); }
            catch (Exception ex) { return default(T); }
 
            // PERFORM PROPERTY DIVE //
 
            String propertyName;
            Object propertyValue;
            Type propertyListType;
            IType entityPropertyType = null;
            Type propertyListInternalType;
            // get properties for this object
            PropertyInfo[] propertyInfos = entityType.GetProperties();
            // loop over source properties & compare
            foreach (PropertyInfo propertyInfo in propertyInfos)
            {
                // get property name
                propertyName = propertyInfo.Name;
                // get property type
                try { entityPropertyType = entityMetadata.GetPropertyType(propertyName); }
                catch (Exception ex) { continue; }
                // get property value
                propertyValue = propertyInfo.GetValue(entity, null);
                // these are not the good kind of bags :P
                if (entityPropertyType.IsCollectionType)
                {
                    // first get the property list's internal type
                    propertyListInternalType = propertyInfo.PropertyType.GetGenericArguments()[0];
                    // create new array type based on the internal type
                    propertyListType = typeof(List<>).MakeGenericType(propertyListInternalType);
                    // create a new property list of the internal type
                    IList propertyList = (IList)Activator.CreateInstance(propertyListType);
                    // set the property list in the resolved object
                    propertyInfo.SetValue(resolvedEntity, propertyList, null);
                    // get the enumerator for this property value
                    IEnumerator enumerator = ((IEnumerable)propertyValue).GetEnumerator();
                    // loop over items to also perform resolution
                    while (enumerator.MoveNext())
                        propertyList.Add(Resolve(enumerator.Current, resolvedEntities));
                }
                // destroy hibernate proxies
                else if (entityPropertyType.IsEntityType)
                {
                    // set the property of the resolved entity to the child beneath us
                    propertyInfo.SetValue(resolvedEntity, Resolve(propertyValue, resolvedEntities), null);
                }
            }
 
            // return the resolved entity :)
            return resolvedEntity;
        }
    }
}

This works FLAWLESSLY for me. When I lazy load or eager load sub-entities before calling Resolve() it perfectly serializes only what I want and does not attempt to lazy load the entire DB.

Let me know if this doesn't work for you :).

Thanks,

Alex G.

WCF + NHibernate: Entity Serialization

awgneo — Sat, 28 Jan 2012 22:22:37 GMT

Revision 3 posted to How to by awgneo on 28/01/2012 07:22:37 p.m.

WCF + NHibernate: Entity Serialization

Filed under: lazy loading, Nhibernate, FluentNH

I found many examples online on covering how to serialize NHibernate entities for use over a WCF channel, while still using lazy and eager loading. In my application, my database models and my SOA models needed to be exactly the same; therefore, I wanted to avoid the use of DTOs. However, none of the examples I found quite worked for me.

Examples I found included:

IDataContractSurrogate (http://www.timvasil.com/blog14/post/2008/02/WCF-serialization-with-NHibernate.aspx) that allows WCF to attempt serialization by walking over the object graph (has a bug that does not allow proper XML generation: http://connect.microsoft.com/wcf/feedback/details/404241/method-object-getobjecttoserialize-object-obj-type-targettype-of-idatacontractsurrogate-can-not-return-null)
Standard Object Graph Walking (http://trentacular.com/2009/08/how-to-use-nhibernate-lazy-initializing-proxies-with-web-services-or-wcf/) this example did not work for me at all, but it was close to my final solution. Additionally, this example does not support collections

My custom object graph walker (I hacked this out of some integrated code so it may need some tweaking):

using System;
using System.Collections.Generic;
using System.Collections;
using System.Reflection;
using System.Data;
using System.Linq;
using System.Configuration;
using FluentNHibernate.Cfg;
using FluentNHibernate.Cfg.Db;
using NHibernate;
using NHibernate.Cfg;
using NHibernate.Tool.hbm2ddl;
using FluentNHibernate.Automapping;
using Radiant.RQS.Services.Types;
using Radiant.RQS.Services.Core.Conventions;
using Radiant.RQS.Superbank;
using NHibernate.Proxy;
using NHibernate.Collection;
using NHibernate.Metadata;
using NHibernate.Type;
 
namespace Radiant.RQS.Services.Core
{
    public static class Resolver
    {
        public static List<T> ResolveList<T>(List<T> entityList, ISession session) where T : class
        {
            // create a resolved entities list for peace and sharing
            List<Object> resolvedEntities = new List<Object>();
            // loop over elements
            for (int entityListIndex = 0; entityListIndex < entityList.Count; entityListIndex++)
                entityList[entityListIndex] = Resolve<T>(entityList[entityListIndex], resolvedEntities, session);
 
            // done
            return entityList;
        }
 
        public static T[] ResolveArray<T>(T[] entityArray, ISession session) where T : class
        {
            // create a resolved entities list for peace and sharing
            List<Object> resolvedEntities = new List<Object>();
            // loop over elements
            for (int entityArrayIndex = 0; entityArrayIndex < entityArray.Length; entityArrayIndex++)
                entityArray[entityArrayIndex] = Resolve<T>(entityArray[entityArrayIndex], resolvedEntities, session);
 
            // done
            return entityArray;
        }
 
        public static T Resolve<T>(T entity, ISession session) where T : class
        {
            // forward to resolver
            return Resolve<T>(entity, new List<Object>(), session);
        }
 
        private static T Resolve<T>(T entity, List<Object> resolvedEntities, ISession session) where T : class
        {
            // CHECKS //
 
            // if the entity is null, just skip it
            if (entity == null)
                return default(T);
            // if we have already resolved it, return that
            if (resolvedEntities.Contains(entity))
                return entity;
 
            // RESOLVE ENTITY //
 
            T resolvedEntity = default(T);
            // now lets go ahead and make sure everything is unproxied
            try { resolvedEntity = (T)session.GetSessionImplementation().PersistenceContext.Unproxy(entity); }
            catch (Exception ex) { return default(T); }
            // add entity to the list of resolved entities
            resolvedEntities.Add(resolvedEntity);
 
            // GET TYPE INFO //
 
            IClassMetadata entityMetadata = null;
            // get the entity type
            Type entityType = entity.GetType();
            // get the entity meta data from the type
            try { entityMetadata = session.SessionFactory.GetClassMetadata(entityType); }
            catch (Exception ex) { return default(T); }
 
            // PERFORM PROPERTY DIVE //
 
            String propertyName;
            Object propertyValue;
            Type propertyListType;
            IType entityPropertyType = null;
            Type propertyListInternalType;
            // get properties for this object
            PropertyInfo[] propertyInfos = entityType.GetProperties();
            // loop over source properties & compare
            foreach (PropertyInfo propertyInfo in propertyInfos)
            {
                // get property name
                propertyName = propertyInfo.Name;
                // get property type
                try { entityPropertyType = entityMetadata.GetPropertyType(propertyName); }
                catch (Exception ex) { continue; }
                // get property value
                propertyValue = propertyInfo.GetValue(entity, null);
                // these are not the good kind of bags :P
                if (entityPropertyType.IsCollectionType)
                {
                    // first get the property list's internal type
                    propertyListInternalType = propertyInfo.PropertyType.GetGenericArguments()[0];
                    // create new array type based on the internal type
                    propertyListType = typeof(List<>).MakeGenericType(propertyListInternalType);
                    // create a new property list of the internal type
                    IList propertyList = (IList)Activator.CreateInstance(propertyListType);
                    // set the property list in the resolved object
                    propertyInfo.SetValue(resolvedEntity, propertyList, null);
                    // get the enumerator for this property value
                    IEnumerator enumerator = ((IEnumerable)propertyValue).GetEnumerator();
                    // loop over items to also perform resolution
                    while (enumerator.MoveNext())
                        propertyList.Add(Resolve(enumerator.Current, resolvedEntities));
                }
                // destroy hibernate proxies
                else if (entityPropertyType.IsEntityType)
                {
                    // set the property of the resolved entity to the child beneath us
                    propertyInfo.SetValue(resolvedEntity, Resolve(propertyValue, resolvedEntities), null);
                }
            }
 
            // return the resolved entity :)
            return resolvedEntity;
        }
    }
}

This works FLAWLESSLY for me. When I lazy load or eager load sub-entities before calling Resolve() it perfectly serializes only what I want and does not attempt to lazy load the entire DB.

Let me know if this doesn't work for you :).

Thanks,

Alex G.

WCF + NHibernate: Entity Serialization

awgneo — Sat, 28 Jan 2012 22:22:19 GMT

Revision 2 posted to How to by awgneo on 28/01/2012 07:22:19 p.m.

WCF + NHibernate: Entity Serialization

Filed under: lazy loading, Nhibernate, FluentNH

I found many example examples online on how to serialize NHibernate entities for use over a WCF channel, while still using lazy and eager loading. In my application, my database models and my SOA models needed to be exactly the same; therefore, I wanted to avoid the use of DTOs. However, none of the examples I found quite worked for me.

Examples I found included:

IDataContractSurrogate (http://www.timvasil.com/blog14/post/2008/02/WCF-serialization-with-NHibernate.aspx) that allows WCF to attempt serialization by walking over the object graph (has a bug that does not allow proper XML generation: http://connect.microsoft.com/wcf/feedback/details/404241/method-object-getobjecttoserialize-object-obj-type-targettype-of-idatacontractsurrogate-can-not-return-null)
Standard Object Graph Walking (http://trentacular.com/2009/08/how-to-use-nhibernate-lazy-initializing-proxies-with-web-services-or-wcf/) this example did not work for me at all, but it was close to my final solution. Additionally, this example does not support collections

My custom object graph walker (I hacked this out of some integrated code so it may need some tweaking):

using System;
using System.Collections.Generic;
using System.Collections;
using System.Reflection;
using System.Data;
using System.Linq;
using System.Configuration;
using FluentNHibernate.Cfg;
using FluentNHibernate.Cfg.Db;
using NHibernate;
using NHibernate.Cfg;
using NHibernate.Tool.hbm2ddl;
using FluentNHibernate.Automapping;
using Radiant.RQS.Services.Types;
using Radiant.RQS.Services.Core.Conventions;
using Radiant.RQS.Superbank;
using NHibernate.Proxy;
using NHibernate.Collection;
using NHibernate.Metadata;
using NHibernate.Type;
 
namespace Radiant.RQS.Services.Core
{
    public static class Resolver
    {
        public static List<T> ResolveList<T>(List<T> entityList, ISession session) where T : class
        {
            // create a resolved entities list for peace and sharing
            List<Object> resolvedEntities = new List<Object>();
            // loop over elements
            for (int entityListIndex = 0; entityListIndex < entityList.Count; entityListIndex++)
                entityList[entityListIndex] = Resolve<T>(entityList[entityListIndex], resolvedEntities, session);
 
            // done
            return entityList;
        }
 
        public static T[] ResolveArray<T>(T[] entityArray, ISession session) where T : class
        {
            // create a resolved entities list for peace and sharing
            List<Object> resolvedEntities = new List<Object>();
            // loop over elements
            for (int entityArrayIndex = 0; entityArrayIndex < entityArray.Length; entityArrayIndex++)
                entityArray[entityArrayIndex] = Resolve<T>(entityArray[entityArrayIndex], resolvedEntities, session);
 
            // done
            return entityArray;
        }
 
        public static T Resolve<T>(T entity, ISession session) where T : class
        {
            // forward to resolver
            return Resolve<T>(entity, new List<Object>(), session);
        }
 
        private static T Resolve<T>(T entity, List<Object> resolvedEntities, ISession session) where T : class
        {
            // CHECKS //
 
            // if the entity is null, just skip it
            if (entity == null)
                return default(T);
            // if we have already resolved it, return that
            if (resolvedEntities.Contains(entity))
                return entity;
 
            // RESOLVE ENTITY //
 
            T resolvedEntity = default(T);
            // now lets go ahead and make sure everything is unproxied
            try { resolvedEntity = (T)session.GetSessionImplementation().PersistenceContext.Unproxy(entity); }
            catch (Exception ex) { return default(T); }
            // add entity to the list of resolved entities
            resolvedEntities.Add(resolvedEntity);
 
            // GET TYPE INFO //
 
            IClassMetadata entityMetadata = null;
            // get the entity type
            Type entityType = entity.GetType();
            // get the entity meta data from the type
            try { entityMetadata = session.SessionFactory.GetClassMetadata(entityType); }
            catch (Exception ex) { return default(T); }
 
            // PERFORM PROPERTY DIVE //
 
            String propertyName;
            Object propertyValue;
            Type propertyListType;
            IType entityPropertyType = null;
            Type propertyListInternalType;
            // get properties for this object
            PropertyInfo[] propertyInfos = entityType.GetProperties();
            // loop over source properties & compare
            foreach (PropertyInfo propertyInfo in propertyInfos)
            {
                // get property name
                propertyName = propertyInfo.Name;
                // get property type
                try { entityPropertyType = entityMetadata.GetPropertyType(propertyName); }
                catch (Exception ex) { continue; }
                // get property value
                propertyValue = propertyInfo.GetValue(entity, null);
                // these are not the good kind of bags :P
                if (entityPropertyType.IsCollectionType)
                {
                    // first get the property list's internal type
                    propertyListInternalType = propertyInfo.PropertyType.GetGenericArguments()[0];
                    // create new array type based on the internal type
                    propertyListType = typeof(List<>).MakeGenericType(propertyListInternalType);
                    // create a new property list of the internal type
                    IList propertyList = (IList)Activator.CreateInstance(propertyListType);
                    // set the property list in the resolved object
                    propertyInfo.SetValue(resolvedEntity, propertyList, null);
                    // get the enumerator for this property value
                    IEnumerator enumerator = ((IEnumerable)propertyValue).GetEnumerator();
                    // loop over items to also perform resolution
                    while (enumerator.MoveNext())
                        propertyList.Add(Resolve(enumerator.Current, resolvedEntities));
                }
                // destroy hibernate proxies
                else if (entityPropertyType.IsEntityType)
                {
                    // set the property of the resolved entity to the child beneath us
                    propertyInfo.SetValue(resolvedEntity, Resolve(propertyValue, resolvedEntities), null);
                }
            }
 
            // return the resolved entity :)
            return resolvedEntity;
        }
    }
}

This works FLAWLESSLY for me. When I lazy load or eager load sub-entities before calling Resolve() it perfectly serializes only what I want and does not attempt to lazy load the entire DB.

Let me know if this doesn't work for you :).

Thanks,

Alex G.

WCF + NHibernate: Entity Serialization

awgneo — Sat, 28 Jan 2012 22:21:48 GMT

Revision 1 posted to How to by awgneo on 28/01/2012 07:21:48 p.m.

I found many example online on how to serialize NHibernate entities for use over a WCF channel, while still using lazy and eager loading. In my application, my database models and my SOA models needed to be exactly the same; therefore, I wanted to avoid the use of DTOs. However, none of the examples I found quite worked for me.

Examples I found included:

IDataContractSurrogate (http://www.timvasil.com/blog14/post/2008/02/WCF-serialization-with-NHibernate.aspx) that allows WCF to attempt serialization by walking over the object graph (has a bug that does not allow proper XML generation: http://connect.microsoft.com/wcf/feedback/details/404241/method-object-getobjecttoserialize-object-obj-type-targettype-of-idatacontractsurrogate-can-not-return-null)
Standard Object Graph Walking (http://trentacular.com/2009/08/how-to-use-nhibernate-lazy-initializing-proxies-with-web-services-or-wcf/) this example did not work for me at all, but it was close to my final solution. Additionally, this example does not support collections

My custom object graph walker (I hacked this out of some integrated code so it may need some tweaking):

using System;
using System.Collections.Generic;
using System.Collections;
using System.Reflection;
using System.Data;
using System.Linq;
using System.Configuration;
using FluentNHibernate.Cfg;
using FluentNHibernate.Cfg.Db;
using NHibernate;
using NHibernate.Cfg;
using NHibernate.Tool.hbm2ddl;
using FluentNHibernate.Automapping;
using Radiant.RQS.Services.Types;
using Radiant.RQS.Services.Core.Conventions;
using Radiant.RQS.Superbank;
using NHibernate.Proxy;
using NHibernate.Collection;
using NHibernate.Metadata;
using NHibernate.Type;
 
namespace Radiant.RQS.Services.Core
{
    public static class Resolver
    {
        public static List<T> ResolveList<T>(List<T> entityList, ISession session) where T : class
        {
            // create a resolved entities list for peace and sharing
            List<Object> resolvedEntities = new List<Object>();
            // loop over elements
            for (int entityListIndex = 0; entityListIndex < entityList.Count; entityListIndex++)
                entityList[entityListIndex] = Resolve<T>(entityList[entityListIndex], resolvedEntities, session);
 
            // done
            return entityList;
        }
 
        public static T[] ResolveArray<T>(T[] entityArray, ISession session) where T : class
        {
            // create a resolved entities list for peace and sharing
            List<Object> resolvedEntities = new List<Object>();
            // loop over elements
            for (int entityArrayIndex = 0; entityArrayIndex < entityArray.Length; entityArrayIndex++)
                entityArray[entityArrayIndex] = Resolve<T>(entityArray[entityArrayIndex], resolvedEntities, session);
 
            // done
            return entityArray;
        }
 
        public static T Resolve<T>(T entity, ISession session) where T : class
        {
            // forward to resolver
            return Resolve<T>(entity, new List<Object>(), session);
        }
 
        private static T Resolve<T>(T entity, List<Object> resolvedEntities, ISession session) where T : class
        {
            // CHECKS //
 
            // if the entity is null, just skip it
            if (entity == null)
                return default(T);
            // if we have already resolved it, return that
            if (resolvedEntities.Contains(entity))
                return entity;
 
            // RESOLVE ENTITY //
 
            T resolvedEntity = default(T);
            // now lets go ahead and make sure everything is unproxied
            try { resolvedEntity = (T)session.GetSessionImplementation().PersistenceContext.Unproxy(entity); }
            catch (Exception ex) { return default(T); }
            // add entity to the list of resolved entities
            resolvedEntities.Add(resolvedEntity);
 
            // GET TYPE INFO //
 
            IClassMetadata entityMetadata = null;
            // get the entity type
            Type entityType = entity.GetType();
            // get the entity meta data from the type
            try { entityMetadata = session.SessionFactory.GetClassMetadata(entityType); }
            catch (Exception ex) { return default(T); }
 
            // PERFORM PROPERTY DIVE //
 
            String propertyName;
            Object propertyValue;
            Type propertyListType;
            IType entityPropertyType = null;
            Type propertyListInternalType;
            // get properties for this object
            PropertyInfo[] propertyInfos = entityType.GetProperties();
            // loop over source properties & compare
            foreach (PropertyInfo propertyInfo in propertyInfos)
            {
                // get property name
                propertyName = propertyInfo.Name;
                // get property type
                try { entityPropertyType = entityMetadata.GetPropertyType(propertyName); }
                catch (Exception ex) { continue; }
                // get property value
                propertyValue = propertyInfo.GetValue(entity, null);
                // these are not the good kind of bags :P
                if (entityPropertyType.IsCollectionType)
                {
                    // first get the property list's internal type
                    propertyListInternalType = propertyInfo.PropertyType.GetGenericArguments()[0];
                    // create new array type based on the internal type
                    propertyListType = typeof(List<>).MakeGenericType(propertyListInternalType);
                    // create a new property list of the internal type
                    IList propertyList = (IList)Activator.CreateInstance(propertyListType);
                    // set the property list in the resolved object
                    propertyInfo.SetValue(resolvedEntity, propertyList, null);
                    // get the enumerator for this property value
                    IEnumerator enumerator = ((IEnumerable)propertyValue).GetEnumerator();
                    // loop over items to also perform resolution
                    while (enumerator.MoveNext())
                        propertyList.Add(Resolve(enumerator.Current, resolvedEntities));
                }
                // destroy hibernate proxies
                else if (entityPropertyType.IsEntityType)
                {
                    // set the property of the resolved entity to the child beneath us
                    propertyInfo.SetValue(resolvedEntity, Resolve(propertyValue, resolvedEntities), null);
                }
            }
 
            // return the resolved entity :)
            return resolvedEntity;
        }
    }
}

This works FLAWLESSLY for me. When I lazy load or eager load sub-entities before calling Resolve() it perfectly serializes only what I want and does not attempt to lazy load the entire DB.

Let me know if this doesn't work for you :).

Thanks,

Alex G.

Mapping tables

oceantrain — Wed, 23 Nov 2011 15:01:29 GMT

Current revision posted to How to by oceantrain on 23/11/2011 12:01:29 p.m.

I'm new to NHibernate, So I'm not sure if I this is even the place to ask questions. But here goes.

This is my problem:

I am building a website using Orchard CMS. All the Orchard tables are mapped by NHibernate. I also have tables in the same database that are NOT mapped by NHibernate. These tables were provided by the client. I need to query these tables and display data on the front end using Orchard. I must keep the table schemas in tact. I have a tutorial on how to map tables using NHibernate, however everything I see in the tutorials, requires the tables to have an ID column as the Primary key. None of the tables provided to me by the client have ID as the first/Primary key column. Is it possible to map to these tables without using the ID method? Or a variation of the ID method?

Id(x => x.Id);

Instead can I map to the table using:

MyColumnName/Primarykey(x => x.Id);

Id(x => x.MyColumnname/PrimaryKey);

Again, at this point I cannot migrate the data into new tables mapped by NHibernate and also the table schema must remain in tact. As the Client is updating these tables on a nightly bases.

Any help is appreciated.

Thanks

Oceantrain

Creating a custom id generator for nHibernate

Steve Bohlen — Sun, 20 Nov 2011 23:29:17 GMT

Current revision posted to How to by Steve Bohlen on 20/11/2011 08:29:17 p.m.

Creating a custom id generator for nHibernate

Filed under: Mapping, Nhibernate, IIdentifierGenerator, IPersistentIdentifierGenerator, TableGenerator, FluentNH

I originally blogged about this here and here on my blog but Fabio suggested I add these posts to the Forge, so here I am. I have to say I am a little exited to make my first contribution to the Wiki [H]. I will try to add a bit more to them and show some examples that do not use the TableGenerator class but directly implement IIdentifierGenerator . Please let me know if there are any mistakes or anything else you want to see.

Before beginning I recommend that you download the NH source code and take a quick look at the TableGenerator , IIdentifierGenerator and IPersistentIdentifierGenerator classes as you will be working with these classes and interfaces to implement your custom generator.

Part 1: Inheriting from TableGenerator class

Currently I am doing some work developing a utility that imports securities data into a fairly old legacy database. It is still SQL but the database and software havn't been updated in about 15 years (maybe more) and never will be again.

The original application for this database uses a primitive hilo-style ID generator mechanism. Tt simply queries an integer value from a table in the database and increments it, then it adds a fixed value to it and uses that as the next unique ID. It doesn't seem very optimal, but that's how it works and there's no changing it.

It isn't complex, but it also isn't one of the identity strategies available in nHibernate and I fully intend to use nHibernate.

So what to do? One option would be to set generator="assigned" and do it all myself, assigning the ID using ADO.Net directly or something similar... but what fun would that be? No, I've decided to take a peak at the nHibernate code and learn to extend it. Read on to find out how to create a custom class that inherits from IIdentifierGenerator to implement your own custom ID generator strategy for nHibernate.

One of the beautiful things about nHibernate the ability to extend it. You can extend its functionality without ever touching their source code.

It was very easy to locate the classes responsible for ID generation in the NHibernate.ID namespace. It was also clear immediately that most classes inherited from IIdentifierGenerator. I also knew that my strategy was similar to the procedure that hilo implements so I started with TableHiLoGenerator which inherts from TableGenerator.

After playing around with this for a while and trying different things, it was clear that TableGenerator, basically takes a tablename and columnname from the configuration, reads a value, increments it and passes it on as an ID. Voila! That was almost exactly what I needed to do with little else to change. I was quickly able to create my own class inheriting from TableGenerator

public class FDPSequence : TableGenerator
{
    private const Int32 SeedValue = 1048576;
 
    private static readonly ILog Log = LogManager.GetLogger(typeof(FDPSequence));
 
    public override object Generate(ISessionImplementor session, object obj)
    {
        int counter = Convert.ToInt32(base.Generate(session, obj));
        return counter + SeedValue + 1;
    }
}

Not much to that is there? Now that is a fairly simple case, but even getting more complex isn't much harder than that. You can implement IIdentifierGenerator directly and create something far more customized. TableGenerator actually implements IPersistentIdentifierGenerator which is an interface for identifiers which need to write and updated value to the database. However, since nHibernate provides so many versatile and inheritable base class generators that you will likely get by with inheriting one of those and extending it as I did.

In order to use this custom generator class I setup my configuration to use it. Using Fluent I wrote a mapping like this:

public class InvestSpecMap : FDPEntityBaseMap<InvestSpec>
{
    public InvestSpecMap()
    {
        WithTable("InvestSpec");
        Id(x => x.Id).ColumnName(tablename + "ID")
            .SetGeneratorClass(typeof(FDPGenerator.FDPSequence).AssemblyQualifiedName)
            .AddGeneratorParam("table", "zSysCounters") //Name of the ID counter table
            .AddGeneratorParam("column", "InvestSpec"); //ID counter column for this table
        Map(x => x.AnnualDividend).ColumnName("AnnlzdDiv");
        Map(x => x.AssetClass);
        Map(x => x.CurrencyType);
        Map(x => x.CusipNumber).ColumnName("CusipNum");
        Map(x => x.DividendFreq).ColumnName("DivFrequency");
        Map(x => x.FullName);
        Map(x => x.MaturityDate).ColumnName("MaturityDt");
        Map(x => x.PriceAsOf).ColumnName("PriceAsOfDt");
        Map(x => x.ShortName).ColumnName("AbbrName");
        Map(x => x.TaxTreatment);
        Map(x => x.TickerSymbol);
        Map(x => x.Type);
        Map(x => x.UnitPrice);
    }
}

You can do the same with XML mappings just declare the assembly and class as you usually would in XML. This is actually the first time I've used FluentNH.

What is great about this is that even when testing my mappings with SQLLite, SchemaExport is actually able to create the identity table based on the tablename and columnname properties in the nHibernate configuration. The main benefit here however is that identity generation remains transparent to the rest of my application. Also doing something cool with nHibernate, that's priceless of course

Part 2: Stealing from TableGenerator and controlling DDL generation

A while ago I posted about writing a custom id generator using nHibernate and extending one of the existing Generator classes nHibernate provides. This was done to support working with a legacy database which uses a custom id generation strategy. One thing I like to do with all my apps is write some basic CRUD tests to make sure my mappings and queries are all working properly.

To do this I use Oren's approach of creating a temporary in-memory database using SQLite to work with. This involves using the SchemaExport tool in nHibernate to generate the DDL to create the database. If you are using a table generator strategy it also needs to create the table and columns for the custom id generator. In some cases you may need to customize the DDL for your Id table.

As I discovered the DDL to generate the table to store the next id value for my custom id is only created once and does not check the column name value for each class. For my id generator there is a separate column used for each table in the database, so this was a problem. For example, the Price table has a column in the Counter table called Price to store it's counter and the Holding table has a column called Holding, but I was only getting one column (this appears to be a problem with hilo and SchemaExport, you can currently only have one column per database)

The TableGenerator class supports two parameters which are set in the HBM files (or using fluent) tablename and columnname which set the table and column names used for the id counter. If you have a copy of the nHibernate source code you will see that the TableGenerator class calls SqlCreateStrings()and SqlDropString() to create and drop the table for the id generator. Unfortunately, as I mentioned above this is only called once, and so it only creates one table with one column for whichever mapping is handled first.

In order to fix this I had to copy the TableGenerator class (yes, yes, I know copy-paste is bad form) and modify those functions. I also added a third parameter allcolumnnames in which I can provide a comma separated list of all the columns the table needs to have (one per table in my database). The SqlCreateStrings()is simple changed to:

public string[] SqlCreateStrings(Dialect dialect) {
  string create = "create table " + tableName + " (";
  string insert = "insert into " + tableName + " values (";
  foreach (string s in allcolumns.Split(',')) {
    create += " " + s + " " + dialect.GetTypeName(columnSqlType) + ",";
    insert += " 1,";
  }
  create = create.Trim(',') + " )";
  insert = insert.Trim(',') + " )";
  return new[] {create, insert};
}

(Yes, yes, I know I should have learned from my last post and used a StringBuilder here as I pointed out in my last post, but seriously, this method will only ever be called once)

Now when it is called it will create the correct table with all the columns I need. A couple of example mappings for the database in FluentNH are shown below:

public InvestSpecMap() {
  WithTable("InvestSpec");
  Id(x => x.Id).ColumnName("InvestSpecID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestSpec"); //ID counter column name

public PriceMap() {
  WithTable("InvestPrice");
  Id(x => x.Id).ColumnName("InvestPriceID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestPrice"); //ID counter column name

To be completely "clean code" and avoid repeating myself I should probably factor out the Id() code into a method in an inhereted base class so I can call it from each mapping class like this:

protected void SetIdGenerator(string tablename) {
  Id(x => x.Id).ColumnName(TableName + "Id")
    .SetGeneratorClass(typeof(FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", AllColumns)
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", TableName); //ID counter column name
}

Now I can unit test using a temporary in-memory SQLite database and all my tests are passing.

Source :

packshot 360

Creating a custom id generator for nHibernate

marcusix — Sun, 20 Nov 2011 22:56:44 GMT

Revision 10 posted to How to by marcusix on 20/11/2011 07:56:44 p.m.

Creating a custom id generator for nHibernate

Filed under: Mapping, Nhibernate, IIdentifierGenerator, IPersistentIdentifierGenerator, TableGenerator, FluentNH

I originally blogged about this here and here on my blog but Fabio suggested I add these posts to the Forge, so here I am.Buy Essay Online I have to say I am a little exited to make my first contribution to the Wiki [H]. I will try to add a bit more to them and show some examples that do not use the TableGenerator class but directly implement IIdentifierGenerator . Please let me know if there are any mistakes or anything else you want to see.Write My Essay For Me

Part 1: Inheriting from TableGenerator class

Cur rently

It isn't complex, but it also isn't one of the identity strategies available in nHibernate and I fully intend to use nHibernate.UK Essay Help

One of the beautiful things about nHibernate the ability to extend it. You can extend its functionality without ever touching their source code.Essay Writing Service

It was very easy to locate the classes responsible for ID generation in the NHibernate.ID namespace. It was also clear immediately that most classes inherited from IIdentifierGenerator.Logo Contests I also knew that my strategy was similar to the procedure that hilo implements so I started with TableHiLoGenerator which inherts from TableGenerator.

public class FDPSequence : TableGenerator
{
    private const Int32 SeedValue = 1048576;
 
    private static readonly ILog Log = LogManager.GetLogger(typeof(FDPSequence));
 
    public override object Generate(ISessionImplementor session, object obj)
    {
        int counter = Convert.ToInt32(base.Generate(session, obj));
        return counter + SeedValue + 1;
    }
}

In order to use this custom generator class I setup my configuration to use it. Using Fluent I wrote a mapping like this:

public class InvestSpecMap : FDPEntityBaseMap<InvestSpec>
{
    public InvestSpecMap()
    {
        WithTable("InvestSpec");
        Id(x => x.Id).ColumnName(tablename + "ID")
            .SetGeneratorClass(typeof(FDPGenerator.FDPSequence).AssemblyQualifiedName)
            .AddGeneratorParam("table", "zSysCounters") //Name of the ID counter table
            .AddGeneratorParam("column", "InvestSpec"); //ID counter column for this table
        Map(x => x.AnnualDividend).ColumnName("AnnlzdDiv");
        Map(x => x.AssetClass);
        Map(x => x.CurrencyType);
        Map(x => x.CusipNumber).ColumnName("CusipNum");
        Map(x => x.DividendFreq).ColumnName("DivFrequency");
        Map(x => x.FullName);
        Map(x => x.MaturityDate).ColumnName("MaturityDt");
        Map(x => x.PriceAsOf).ColumnName("PriceAsOfDt");
        Map(x => x.ShortName).ColumnName("AbbrName");
        Map(x => x.TaxTreatment);
        Map(x => x.TickerSymbol);
        Map(x => x.Type);
        Map(x => x.UnitPrice);
    }
}

You can do the same with XML mappings just declare the assembly and class as you usually would in XML. This is actually the first time I've used FluentNH.

Part 2: Stealing from TableGenerator and controlling DDL generation

public string[] SqlCreateStrings(Dialect dialect) {
  string create = "create table " + tableName + " (";
  string insert = "insert into " + tableName + " values (";
  foreach (string s in allcolumns.Split(',')) {
    create += " " + s + " " + dialect.GetTypeName(columnSqlType) + ",";
    insert += " 1,";
  }
  create = create.Trim(',') + " )";
  insert = insert.Trim(',') + " )";
  return new[] {create, insert};
}

(Yes, yes, I know I should have learned from my last post and used a StringBuilder here as I pointed out in my last post, but seriously, this method will only ever be called once)

Now when it is called it will create the correct table with all the columns I need. A couple of example mappings for the database in FluentNH are shown below:

public InvestSpecMap() {
  WithTable("InvestSpec");
  Id(x => x.Id).ColumnName("InvestSpecID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestSpec"); //ID counter column name

public PriceMap() {
  WithTable("InvestPrice");
  Id(x => x.Id).ColumnName("InvestPriceID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestPrice"); //ID counter column name

To be completely "clean code" and avoid repeating myself I should probably factor out the Id() code into a method in an inhereted base class so I can call it from each mapping class like this:

protected void SetIdGenerator(string tablename) {
  Id(x => x.Id).ColumnName(TableName + "Id")
    .SetGeneratorClass(typeof(FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", AllColumns)
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", TableName); //ID counter column name
}

Now I can unit test using a temporary in-memory SQLite database and all my tests are passing.

Source :

packshot 360

Creating a custom id generator for nHibernate

smithwilsonrogard — Wed, 12 Oct 2011 10:43:32 GMT

Revision 9 posted to How to by smithwilsonrogard on 12/10/2011 07:43:32 a.m.

Creating a custom id generator for nHibernate

Filed under: Mapping, Nhibernate, IIdentifierGenerator, IPersistentIdentifierGenerator, TableGenerator, FluentNH

Part 1: Inheriting from TableGenerator class

It isn't complex, but it also isn't one of the identity strategies available in nHibernate and I fully intend to use nHibernate.UK Essay Help

One of the beautiful things about nHibernate the ability to extend it. You can extend its functionality without ever touching their source code.Essay Writing Service

It was very easy to locate the classes responsible for ID generation in the NHibernate.ID namespace. It was also clear immediately that most classes inherited from IIdentifierGenerator.Logo Contests I also knew that my strategy was similar to the procedure that hilo implements so I started with TableHiLoGenerator which inherts from TableGenerator.

public class FDPSequence : TableGenerator
{
    private const Int32 SeedValue = 1048576;
 
    private static readonly ILog Log = LogManager.GetLogger(typeof(FDPSequence));
 
    public override object Generate(ISessionImplementor session, object obj)
    {
        int counter = Convert.ToInt32(base.Generate(session, obj));
        return counter + SeedValue + 1;
    }
}

In order to use this custom generator class I setup my configuration to use it. Using Fluent I wrote a mapping like this:

public class InvestSpecMap : FDPEntityBaseMap<InvestSpec>
{
    public InvestSpecMap()
    {
        WithTable("InvestSpec");
        Id(x => x.Id).ColumnName(tablename + "ID")
            .SetGeneratorClass(typeof(FDPGenerator.FDPSequence).AssemblyQualifiedName)
            .AddGeneratorParam("table", "zSysCounters") //Name of the ID counter table
            .AddGeneratorParam("column", "InvestSpec"); //ID counter column for this table
        Map(x => x.AnnualDividend).ColumnName("AnnlzdDiv");
        Map(x => x.AssetClass);
        Map(x => x.CurrencyType);
        Map(x => x.CusipNumber).ColumnName("CusipNum");
        Map(x => x.DividendFreq).ColumnName("DivFrequency");
        Map(x => x.FullName);
        Map(x => x.MaturityDate).ColumnName("MaturityDt");
        Map(x => x.PriceAsOf).ColumnName("PriceAsOfDt");
        Map(x => x.ShortName).ColumnName("AbbrName");
        Map(x => x.TaxTreatment);
        Map(x => x.TickerSymbol);
        Map(x => x.Type);
        Map(x => x.UnitPrice);
    }
}

You can do the same with XML mappings just declare the assembly and class as you usually would in XML. This is actually the first time I've used FluentNH.

Part 2: Stealing from TableGenerator and controlling DDL generation

public string[] SqlCreateStrings(Dialect dialect) {
  string create = "create table " + tableName + " (";
  string insert = "insert into " + tableName + " values (";
  foreach (string s in allcolumns.Split(',')) {
    create += " " + s + " " + dialect.GetTypeName(columnSqlType) + ",";
    insert += " 1,";
  }
  create = create.Trim(',') + " )";
  insert = insert.Trim(',') + " )";
  return new[] {create, insert};
}

(Yes, yes, I know I should have learned from my last post and used a StringBuilder here as I pointed out in my last post, but seriously, this method will only ever be called once)

Now when it is called it will create the correct table with all the columns I need. A couple of example mappings for the database in FluentNH are shown below:

public InvestSpecMap() {
  WithTable("InvestSpec");
  Id(x => x.Id).ColumnName("InvestSpecID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestSpec"); //ID counter column name

public PriceMap() {
  WithTable("InvestPrice");
  Id(x => x.Id).ColumnName("InvestPriceID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestPrice"); //ID counter column name

To be completely "clean code" and avoid repeating myself I should probably factor out the Id() code into a method in an inhereted base class so I can call it from each mapping class like this:

protected void SetIdGenerator(string tablename) {
  Id(x => x.Id).ColumnName(TableName + "Id")
    .SetGeneratorClass(typeof(FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", AllColumns)
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", TableName); //ID counter column name
}

Now I can unit test using a temporary in-memory SQLite database and all my tests are passing.

Creating a custom id generator for nHibernate

suedallin — Wed, 06 Apr 2011 16:58:15 GMT

Revision 8 posted to How to by suedallin on 06/04/2011 01:58:15 p.m.

Creating a custom id generator for nHibernate

Filed under: Mapping, Nhibernate, IIdentifierGenerator, IPersistentIdentifierGenerator, TableGenerator, FluentNH

Part 1: Inheriting from TableGenerator class

Currently

It isn't complex, but it also isn't one of the identity strategies available in nHibernate and I fully intend to use nHibernate.

One of the beautiful things about nHibernate the ability to extend it. You can extend its functionality without ever touching their source code.

It was very easy to locate the classes responsible for ID generation in the NHibernate.ID namespace. It was also clear immediately that most classes inherited from IIdentifierGenerator. I also knew that my strategy was similar to the procedure that hilo implements so I started with TableHiLoGenerator which inherts from TableGenerator.

public class FDPSequence : TableGenerator
{
    private const Int32 SeedValue = 1048576;
 
    private static readonly ILog Log = LogManager.GetLogger(typeof(FDPSequence));
 
    public override object Generate(ISessionImplementor session, object obj)
    {
        int counter = Convert.ToInt32(base.Generate(session, obj));
        return counter + SeedValue + 1;
    }
}

In order to use this custom generator class I setup my configuration to use it. Using Fluent I wrote a mapping like this:

public class InvestSpecMap : FDPEntityBaseMap<InvestSpec>
{
    public InvestSpecMap()
    {
        WithTable("InvestSpec");
        Id(x => x.Id).ColumnName(tablename + "ID")
            .SetGeneratorClass(typeof(FDPGenerator.FDPSequence).AssemblyQualifiedName)
            .AddGeneratorParam("table", "zSysCounters") //Name of the ID counter table
            .AddGeneratorParam("column", "InvestSpec"); //ID counter column for this table
        Map(x => x.AnnualDividend).ColumnName("AnnlzdDiv");
        Map(x => x.AssetClass);
        Map(x => x.CurrencyType);
        Map(x => x.CusipNumber).ColumnName("CusipNum");
        Map(x => x.DividendFreq).ColumnName("DivFrequency");
        Map(x => x.FullName);
        Map(x => x.MaturityDate).ColumnName("MaturityDt");
        Map(x => x.PriceAsOf).ColumnName("PriceAsOfDt");
        Map(x => x.ShortName).ColumnName("AbbrName");
        Map(x => x.TaxTreatment);
        Map(x => x.TickerSymbol);
        Map(x => x.Type);
        Map(x => x.UnitPrice);
    }
}

You can do the same with XML mappings just declare the assembly and class as you usually would in XML. This is actually the first time I've used FluentNH.

Part 2: Stealing from TableGenerator and controlling DDL generation

public string[] SqlCreateStrings(Dialect dialect) {
  string create = "create table " + tableName + " (";
  string insert = "insert into " + tableName + " values (";
  foreach (string s in allcolumns.Split(',')) {
    create += " " + s + " " + dialect.GetTypeName(columnSqlType) + ",";
    insert += " 1,";
  }
  create = create.Trim(',') + " )";
  insert = insert.Trim(',') + " )";
  return new[] {create, insert};
}

(Yes, yes, I know I should have learned from my last post and used a StringBuilder here as I pointed out in my last post, but seriously, this method will only ever be called once)

Now when it is called it will create the correct table with all the columns I need. A couple of example mappings for the database in FluentNH are shown below:

public InvestSpecMap() {
  WithTable("InvestSpec");
  Id(x => x.Id).ColumnName("InvestSpecID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestSpec"); //ID counter column name

public PriceMap() {
  WithTable("InvestPrice");
  Id(x => x.Id).ColumnName("InvestPriceID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestPrice"); //ID counter column name

To be completely "clean code" and avoid repeating myself I should probably factor out the Id() code into a method in an inhereted base class so I can call it from each mapping class like this:

protected void SetIdGenerator(string tablename) {
  Id(x => x.Id).ColumnName(TableName + "Id")
    .SetGeneratorClass(typeof(FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", AllColumns)
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", TableName); //ID counter column name
}

Now I can unit test using a temporary in-memory SQLite database and all my tests are passing.

Creating a custom id generator for nHibernate

markweee — Wed, 30 Mar 2011 11:46:10 GMT

Revision 7 posted to How to by markweee on 30/03/2011 08:46:10 a.m.

Creating a custom id generator for nHibernate

Filed under: Mapping, Nhibernate, IIdentifierGenerator, IPersistentIdentifierGenerator, TableGenerator, FluentNH

Part 1: Inheriting from TableGenerator class

It isn't complex, but it also isn't one of the identity strategies available in nHibernate and I fully intend to use nHibernate.

One of the beautiful things about nHibernate the ability to extend it. You can extend its functionality without ever touching their source code.

It was very easy to locate the classes responsible for ID generation in the NHibernate.ID namespace. It was also clear immediately that most classes inherited from IIdentifierGenerator. I also knew that my strategy was similar to the procedure that hilo implements so I started with TableHiLoGenerator which inherts from TableGenerator.

public class FDPSequence : TableGenerator
{
    private const Int32 SeedValue = 1048576;
 
    private static readonly ILog Log = LogManager.GetLogger(typeof(FDPSequence));
 
    public override object Generate(ISessionImplementor session, object obj)
    {
        int counter = Convert.ToInt32(base.Generate(session, obj));
        return counter + SeedValue + 1;
    }
}

In order to use this custom generator class I setup my configuration to use it. Using Fluent I wrote a mapping like this:

public class InvestSpecMap : FDPEntityBaseMap<InvestSpec>
{
    public InvestSpecMap()
    {
        WithTable("InvestSpec");
        Id(x => x.Id).ColumnName(tablename + "ID")
            .SetGeneratorClass(typeof(FDPGenerator.FDPSequence).AssemblyQualifiedName)
            .AddGeneratorParam("table", "zSysCounters") //Name of the ID counter table
            .AddGeneratorParam("column", "InvestSpec"); //ID counter column for this table
        Map(x => x.AnnualDividend).ColumnName("AnnlzdDiv");
        Map(x => x.AssetClass);
        Map(x => x.CurrencyType);
        Map(x => x.CusipNumber).ColumnName("CusipNum");
        Map(x => x.DividendFreq).ColumnName("DivFrequency");
        Map(x => x.FullName);
        Map(x => x.MaturityDate).ColumnName("MaturityDt");
        Map(x => x.PriceAsOf).ColumnName("PriceAsOfDt");
        Map(x => x.ShortName).ColumnName("AbbrName");
        Map(x => x.TaxTreatment);
        Map(x => x.TickerSymbol);
        Map(x => x.Type);
        Map(x => x.UnitPrice);
    }
}

You can do the same with XML mappings just declare the assembly and class as you usually would in XML. This is actually the first time I've used FluentNH.

Part 2: Stealing from TableGenerator and controlling DDL generation

public string[] SqlCreateStrings(Dialect dialect) {
  string create = "create table " + tableName + " (";
  string insert = "insert into " + tableName + " values (";
  foreach (string s in allcolumns.Split(',')) {
    create += " " + s + " " + dialect.GetTypeName(columnSqlType) + ",";
    insert += " 1,";
  }
  create = create.Trim(',') + " )";
  insert = insert.Trim(',') + " )";
  return new[] {create, insert};
}

(Yes, yes, I know I should have learned from my last post and used a StringBuilder here as I pointed out in my last post, but seriously, this method will only ever be called once)

Now when it is called it will create the correct table with all the columns I need. A couple of example mappings for the database in FluentNH are shown below:

public InvestSpecMap() {
  WithTable("InvestSpec");
  Id(x => x.Id).ColumnName("InvestSpecID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestSpec"); //ID counter column name

public PriceMap() {
  WithTable("InvestPrice");
  Id(x => x.Id).ColumnName("InvestPriceID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestPrice"); //ID counter column name

To be completely "clean code" and avoid repeating myself I should probably factor out the Id() code into a method in an inhereted base class so I can call it from each mapping class like this:

protected void SetIdGenerator(string tablename) {
  Id(x => x.Id).ColumnName(TableName + "Id")
    .SetGeneratorClass(typeof(FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", AllColumns)
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", TableName); //ID counter column name
}

Now I can unit test using a temporary in-memory SQLite database and all my tests are passing.

Creating a custom id generator for nHibernate

Chris Nicola — Sat, 03 Apr 2010 18:14:59 GMT

Revision 6 posted to How to by Chris Nicola on 03/04/2010 03:14:59 p.m.

Creating a custom id generator for nHibernate

Filed under: Mapping, Nhibernate, IIdentifierGenerator, IPersistentIdentifierGenerator, TableGenerator, FluentNH

Part 1: Inheriting from TableGenerator class

It isn't complex, but it also isn't one of the identity strategies available in nHibernate and I fully intend to use nHibernate.

One of the beautiful things about nHibernate the ability to extend it. You can extend its functionality without ever touching their source code.

It was very easy to locate the classes responsible for ID generation in the NHibernate.ID namespace. It was also clear immediately that most classes inherited from IIdentifierGenerator. I also knew that my strategy was similar to the procedure that hilo implements so I started with TableHiLoGenerator which inherts from TableGenerator.

public class FDPSequence : TableGenerator
{
    private const Int32 SeedValue = 1048576;
 
    private static readonly ILog Log = LogManager.GetLogger(typeof(FDPSequence));
 
    public override object Generate(ISessionImplementor session, object obj)
    {
        int counter = Convert.ToInt32(base.Generate(session, obj));
        return counter + SeedValue + 1;
    }
}

In order to use this custom generator class I setup my configuration to use it. Using Fluent I wrote a mapping like this:

public class InvestSpecMap : FDPEntityBaseMap<InvestSpec>
{
    public InvestSpecMap()
    {
        WithTable("InvestSpec");
        Id(x => x.Id).ColumnName(tablename + "ID")
            .SetGeneratorClass(typeof(FDPGenerator.FDPSequence).AssemblyQualifiedName)
            .AddGeneratorParam("table", "zSysCounters") //Name of the ID counter table
            .AddGeneratorParam("column", "InvestSpec"); //ID counter column for this table
        Map(x => x.AnnualDividend).ColumnName("AnnlzdDiv");
        Map(x => x.AssetClass);
        Map(x => x.CurrencyType);
        Map(x => x.CusipNumber).ColumnName("CusipNum");
        Map(x => x.DividendFreq).ColumnName("DivFrequency");
        Map(x => x.FullName);
        Map(x => x.MaturityDate).ColumnName("MaturityDt");
        Map(x => x.PriceAsOf).ColumnName("PriceAsOfDt");
        Map(x => x.ShortName).ColumnName("AbbrName");
        Map(x => x.TaxTreatment);
        Map(x => x.TickerSymbol);
        Map(x => x.Type);
        Map(x => x.UnitPrice);
    }
}

You can do the same with XML mappings just declare the assembly and class as you usually would in XML. This is actually the first time I've used FluentNH.

Part 2: Stealing from TableGenerator and controlling DDL generation

public string[] SqlCreateStrings(Dialect dialect) {
  string create = "create table " + tableName + " (";
  string insert = "insert into " + tableName + " values (";
  foreach (string s in allcolumns.Split(',')) {
    create += " " + s + " " + dialect.GetTypeName(columnSqlType) + ",";
    insert += " 1,";
  }
  create = create.Trim(',') + " )";
  insert = insert.Trim(',') + " )";
  return new[] {create, insert};
}

(Yes, yes, I know I should have learned from my last post and used a StringBuilder here as I pointed out in my last post, but seriously, this method will only ever be called once)

Now when it is called it will create the correct table with all the columns I need. A couple of example mappings for the database in FluentNH are shown below:

public InvestSpecMap() {
  WithTable("InvestSpec");
  Id(x => x.Id).ColumnName("InvestSpecID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestSpec"); //ID counter column name

public PriceMap() {
  WithTable("InvestPrice");
  Id(x => x.Id).ColumnName("InvestPriceID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestPrice"); //ID counter column name

To be completely "clean code" and avoid repeating myself I should probably factor out the Id() code into a method in an inhereted base class so I can call it from each mapping class like this:

protected void SetIdGenerator(string tablename) {
  Id(x => x.Id).ColumnName(TableName + "Id")
    .SetGeneratorClass(typeof(FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", AllColumns)
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", TableName); //ID counter column name
}

Now I can unit test using a temporary in-memory SQLite database and all my tests are passing.

Creating a custom id generator for nHibernate

Chris Nicola — Fri, 25 Dec 2009 00:31:36 GMT

Revision 5 posted to How to by Chris Nicola on 24/12/2009 09:31:36 p.m.

Creating a custom id generator for nHibernate

Filed under: Mapping, Nhibernate, IIdentifierGenerator, IPersistentIdentifierGenerator, TableGenerator, FluentNH

Part 1: Inheriting from TableGenerator class

It isn't complex, but it also isn't one of the identity strategies available in nHibernate and I fully intend to use nHibernate.

One of the beautiful things about nHibernate the ability to extend it. You can extend its functionality without ever touching their source code.

It was very easy to locate the classes responsible for ID generation in the NHibernate.ID namespace. It was also clear immediately that most classes inherited from IIdentifierGenerator. I also knew that my strategy was similar to the procedure that hilo implements so I started with TableHiLoGenerator which inherts from TableGenerator.

public class FDPSequence : TableGenerator
{
    private const Int32 SeedValue = 1048576;
 
    private static readonly ILog Log = LogManager.GetLogger(typeof(FDPSequence));
 
    public override object Generate(ISessionImplementor session, object obj)
    {
        int counter = Convert.ToInt32(base.Generate(session, obj));
        return counter + SeedValue + 1;
    }
}

In order to use this custom generator class I setup my configuration to use it. Using Fluent I wrote a mapping like this:

public class InvestSpecMap : FDPEntityBaseMap<InvestSpec>
{
    public InvestSpecMap()
    {
        WithTable("InvestSpec");
        Id(x => x.Id).ColumnName(tablename + "ID")
            .SetGeneratorClass(typeof(FDPGenerator.FDPSequence).AssemblyQualifiedName)
            .AddGeneratorParam("table", "zSysCounters") //Name of the ID counter table
            .AddGeneratorParam("column", "InvestSpec"); //ID counter column for this table
        Map(x => x.AnnualDividend).ColumnName("AnnlzdDiv");
        Map(x => x.AssetClass);
        Map(x => x.CurrencyType);
        Map(x => x.CusipNumber).ColumnName("CusipNum");
        Map(x => x.DividendFreq).ColumnName("DivFrequency");
        Map(x => x.FullName);
        Map(x => x.MaturityDate).ColumnName("MaturityDt");
        Map(x => x.PriceAsOf).ColumnName("PriceAsOfDt");
        Map(x => x.ShortName).ColumnName("AbbrName");
        Map(x => x.TaxTreatment);
        Map(x => x.TickerSymbol);
        Map(x => x.Type);
        Map(x => x.UnitPrice);
    }
}

You can do the same with XML mappings just declare the assembly and class as you usually would in XML. This is actually the first time I've used FluentNH.

Part 2: Stealing from TableGenerator and controlling DDL generation

As I discovered the code DDL to generate the table to store the next id value for a my custom id is only run created once per class (and then only on does not check the base column name value for each classif you are inheriting). For my id generator there is a separate column used for each table in the database. So, for so this was a problem. For example, the Price table has a column in the Counter table called Price to store it's counter and the Holding table has a column called Holding., but I was only getting one column (this appears to be a problem with hilo and SchemaExport, you can currently only have one column per database)

public string[] SqlCreateStrings(Dialect dialect) {
  string create = "create table " + tableName + " (";
  string insert = "insert into " + tableName + " values (";
  foreach (string s in allcolumns.Split(',')) {
    create += " " + s + " " + dialect.GetTypeName(columnSqlType) + ",";
    insert += " 1,";
  }
  create = create.Trim(',') + " )";
  insert = insert.Trim(',') + " )";
  return new[] {create, insert};
}

(Yes, yes, I know I should have learned from my last post and used a StringBuilder here as I pointed out in my last post, but seriously, this method will only ever be called once)

Now when it is called it will create the correct table with all the columns I need. A couple of example mappings for the database in FluentNH are shown below:

public InvestSpecMap() {
  WithTable("InvestSpec");
  Id(x => x.Id).ColumnName("InvestSpecID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestSpec"); //ID counter column name

public PriceMap() {
  WithTable("InvestPrice");
  Id(x => x.Id).ColumnName("InvestPriceID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestPrice"); //ID counter column name

To be completely "clean code" and avoid repeating myself I should probably factor out the Id() code into a method in an inhereted base class so I can call it from each mapping class like this:

protected void SetIdGenerator(string tablename) {
  Id(x => x.Id).ColumnName(TableName + "Id")
    .SetGeneratorClass(typeof(FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", AllColumns)
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", TableName); //ID counter column name
}

Now I can unit test using a temporary in-memory SQLite database and all my tests are passing.

Creating a custom id generator for nHibernate

Chris Nicola — Fri, 25 Dec 2009 00:25:51 GMT

Revision 4 posted to How to by Chris Nicola on 24/12/2009 09:25:51 p.m.

Creating a custom id generator for nHibernate

Filed under: Mapping, Nhibernate, IIdentifierGenerator, IPersistentIdentifierGenerator, TableGenerator, FluentNH

Part 1: Inheriting from TableGenerator class

It isn't complex, but it also isn't one of the identity strategies available in nHibernate and I fully intend to use nHibernate.

One of the beautiful things about nHibernate the ability to extend it. You can extend its functionality without ever touching their source code.

It was very easy to locate the classes responsible for ID generation in the NHibernate.ID namespace. It was also clear immediately that most classes inherited from IIdentifierGenerator. I also knew that my strategy was similar to the procedure that hilo implements so I started with TableHiLoGenerator which inherts from TableGenerator.

public class FDPSequence : TableGenerator
{
    private const Int32 SeedValue = 1048576;
 
    private static readonly ILog Log = LogManager.GetLogger(typeof(FDPSequence));
 
    public override object Generate(ISessionImplementor session, object obj)
    {
        int counter = Convert.ToInt32(base.Generate(session, obj));
        return counter + SeedValue + 1;
    }
}

In order to use this custom generator class I setup my configuration to use it. Using Fluent I wrote a mapping like this:

public class InvestSpecMap : FDPEntityBaseMap<InvestSpec>
{
    public InvestSpecMap()
    {
        WithTable("InvestSpec");
        Id(x => x.Id).ColumnName(tablename + "ID")
            .SetGeneratorClass(typeof(FDPGenerator.FDPSequence).AssemblyQualifiedName)
            .AddGeneratorParam("table", "zSysCounters") //Name of the ID counter table
            .AddGeneratorParam("column", "InvestSpec"); //ID counter column for this table
        Map(x => x.AnnualDividend).ColumnName("AnnlzdDiv");
        Map(x => x.AssetClass);
        Map(x => x.CurrencyType);
        Map(x => x.CusipNumber).ColumnName("CusipNum");
        Map(x => x.DividendFreq).ColumnName("DivFrequency");
        Map(x => x.FullName);
        Map(x => x.MaturityDate).ColumnName("MaturityDt");
        Map(x => x.PriceAsOf).ColumnName("PriceAsOfDt");
        Map(x => x.ShortName).ColumnName("AbbrName");
        Map(x => x.TaxTreatment);
        Map(x => x.TickerSymbol);
        Map(x => x.Type);
        Map(x => x.UnitPrice);
    }
}

You can do the same with XML mappings just declare the assembly and class as you usually would in XML. This is actually the first time I've used FluentNH.

Part 2: Stealing from TableGenerator and controlling DDL generation

As I discovered the code to generate the table for a custom id is only run once per class (and then only on the base class if you are inheriting). For my id generator there is a separate column used for each table in the database. So, for example the Price table has a column in the Counter table called Price to store it's counter and the Holding table has a column called Holding.

public string[] SqlCreateStrings(Dialect dialect) {
  string create = "create table " + tableName + " (";
  string insert = "insert into " + tableName + " values (";
  foreach (string s in allcolumns.Split(',')) {
    create += " " + s + " " + dialect.GetTypeName(columnSqlType) + ",";
    insert += " 1,";
  }
  create = create.Trim(',') + " )";
  insert = insert.Trim(',') + " )";
  return new[] {create, insert};
}

(Yes, yes, I know I should have learned from my last post and used a StringBuilder here as I pointed out in my last post, but seriously, this method will only ever be called once)

Now when it is called it will create the correct table with all the columns I need. A couple of example mappings for the database in FluentNH are shown below:

public InvestSpecMap() {
  WithTable("InvestSpec");
  Id(x => x.Id).ColumnName("InvestSpecID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestSpec"); //ID counter column name

public PriceMap() {
  WithTable("InvestPrice");
  Id(x => x.Id).ColumnName("InvestPriceID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestPrice"); //ID counter column name

To be completely "clean code" and avoid repeating myself I should probably factor out the Id() code into a method in an inhereted base class so I can call it from each mapping class like this:

protected void SetIdGenerator(string tablename) {
  Id(x => x.Id).ColumnName(TableName + "Id")
    .SetGeneratorClass(typeof(FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", AllColumns)
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", TableName); //ID counter column name
}

Now I can unit test using a temporary in-memory SQLite database and all my tests are passing.

Creating a custom id generator for nHibernate

Chris Nicola — Fri, 25 Dec 2009 00:18:06 GMT

Revision 3 posted to How to by Chris Nicola on 24/12/2009 09:18:06 p.m.

Creating a custom id generator for nHibernate

Filed under: Mapping, Nhibernate, IIdentifierGenerator, IPersistentIdentifierGenerator, TableGenerator, FluentNH

Part 1: Inheriting from TableGenerator class

It isn't complex, but it also isn't one of the identity strategies available in nHibernate and I fully intend to use nHibernate.

One of the beautiful things about nHibernate the ability to extend it. You can extend its functionality without ever touching their source code.

It was very easy to locate the classes responsible for ID generation in the NHibernate.ID namespace. It was also clear immediately that most classes inherited from IIdentifierGenerator. I also knew that my strategy was similar to the procedure that hilo implements so I started with TableHiLoGenerator which inherts from TableGenerator.

public class FDPSequence : TableGenerator
{
    private const Int32 SeedValue = 1048576;
 
    private static readonly ILog Log = LogManager.GetLogger(typeof(FDPSequence));
 
    public override object Generate(ISessionImplementor session, object obj)
    {
        int counter = Convert.ToInt32(base.Generate(session, obj));
        return counter + SeedValue + 1;
    }
}

In order to use this custom generator class I setup my configuration to use it. Using Fluent I wrote a mapping like this:

public class InvestSpecMap : FDPEntityBaseMap<InvestSpec>
{
    public InvestSpecMap()
    {
        WithTable("InvestSpec");
        Id(x => x.Id).ColumnName(tablename + "ID")
            .SetGeneratorClass(typeof(FDPGenerator.FDPSequence).AssemblyQualifiedName)
            .AddGeneratorParam("table", "zSysCounters") //Name of the ID counter table
            .AddGeneratorParam("column", "InvestSpec"); //ID counter column for this table
        Map(x => x.AnnualDividend).ColumnName("AnnlzdDiv");
        Map(x => x.AssetClass);
        Map(x => x.CurrencyType);
        Map(x => x.CusipNumber).ColumnName("CusipNum");
        Map(x => x.DividendFreq).ColumnName("DivFrequency");
        Map(x => x.FullName);
        Map(x => x.MaturityDate).ColumnName("MaturityDt");
        Map(x => x.PriceAsOf).ColumnName("PriceAsOfDt");
        Map(x => x.ShortName).ColumnName("AbbrName");
        Map(x => x.TaxTreatment);
        Map(x => x.TickerSymbol);
        Map(x => x.Type);
        Map(x => x.UnitPrice);
    }
}

You can do the same with XML mappings just declare the assembly and class as you usually would in XML. This is actually the first time I've used FluentNH.

Part 2: Stealing from TableGenerator and controlling DDL generation

public string[] SqlCreateStrings(Dialect dialect) {
  string create = "create table " + tableName + " (";
  string insert = "insert into " + tableName + " values (";
  foreach (string s in allcolumns.Split(',')) {
    create += " " + s + " " + dialect.GetTypeName(columnSqlType) + ",";
    insert += " 1,";
  }
  create = create.Trim(',') + " )";
  insert = insert.Trim(',') + " )";
  return new[] {create, insert};
}

(Yes, yes, I know I should have learned from my last post and used a StringBuilder here as I pointed out in my last post, but seriously, this method will only ever be called once)

Now when it is called it will create the correct table with all the columns I need. A couple of example mappings for the database in FluentNH are shown below:

public InvestSpecMap() {
  WithTable("InvestSpec");
  Id(x => x.Id).ColumnName("InvestSpecID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestSpec"); //ID counter column name

public PriceMap() {
  WithTable("InvestPrice");
  Id(x => x.Id).ColumnName("InvestPriceID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestPrice"); //ID counter column name

To be completely "clean code" and avoid repeating myself I should probably factor out the Id() code into a method in an inhereted base class so I can call it from each mapping class like this:

protected void SetIdGenerator(string tablename) {
  Id(x => x.Id).ColumnName(TableName + "Id")
    .SetGeneratorClass(typeof(FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", AllColumns)
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", TableName); //ID counter column name
}

Now I can unit test using a temporary in-memory SQLite database and all my tests are passing.

Creating a custom id generator for nHibernate

Chris Nicola — Thu, 03 Sep 2009 16:42:06 GMT

Revision 2 posted to How to by Chris Nicola on 03/09/2009 01:42:06 p.m.

Creating a custom id generator for nHibernate

Filed under: Mapping, Nhibernate, IIdentifierGenerator, IPersistentIdentifierGenerator, TableGenerator, FluentNH

Part 1: Inheriting from TableGenerator class

It isn't complex, but it also isn't one of the identity strategies available in nHibernate and I fully intend to use nHibernate.

One of the beautiful things about nHibernate the ability to extend it. You can extend its functionality without ever touching their source code.

It was very easy to locate the classes responsible for ID generation in the NHibernate.ID namespace. It was also clear immediately that most classes inherited from IIdentifierGenerator. I also knew that my strategy was similar to the procedure that hilo implements so I started with TableHiLoGenerator which inherts from TableGenerator.

public class FDPSequence : TableGenerator
{
    private const Int32 SeedValue = 1048576;
 
    private static readonly ILog Log = LogManager.GetLogger(typeof(FDPSequence));
 
    public override object Generate(ISessionImplementor session, object obj)
    {
        int counter = Convert.ToInt32(base.Generate(session, obj));
        return counter + SeedValue + 1;
    }
}

In order to use this custom generator class I setup my configuration to use it. Using Fluent I wrote a mapping like this:

public class InvestSpecMap : FDPEntityBaseMap<InvestSpec>
{
    public InvestSpecMap()
    {
        WithTable("InvestSpec");
        Id(x => x.Id).ColumnName(tablename + "ID")
            .SetGeneratorClass(typeof(FDPGenerator.FDPSequence).AssemblyQualifiedName)
            .AddGeneratorParam("table", "zSysCounters") //Name of the ID counter table
            .AddGeneratorParam("column", "InvestSpec"); //ID counter column for this table
        Map(x => x.AnnualDividend).ColumnName("AnnlzdDiv");
        Map(x => x.AssetClass);
        Map(x => x.CurrencyType);
        Map(x => x.CusipNumber).ColumnName("CusipNum");
        Map(x => x.DividendFreq).ColumnName("DivFrequency");
        Map(x => x.FullName);
        Map(x => x.MaturityDate).ColumnName("MaturityDt");
        Map(x => x.PriceAsOf).ColumnName("PriceAsOfDt");
        Map(x => x.ShortName).ColumnName("AbbrName");
        Map(x => x.TaxTreatment);
        Map(x => x.TickerSymbol);
        Map(x => x.Type);
        Map(x => x.UnitPrice);
    }
}

You can do the same with XML mappings just declare the assembly and class as you usually would in XML. This is actually the first time I've used FluentNH.

Part 2: Stealing from TableGenerator and controlling DDL generation

public string[] SqlCreateStrings(Dialect dialect) {
  string create = "create table " + tableName + " (";
  string insert = "insert into " + tableName + " values (";
  foreach (string s in allcolumns.Split(',')) {
    create += " " + s + " " + dialect.GetTypeName(columnSqlType) + ",";
    insert += " 1,";
  }
  create = create.Trim(',') + " )";
  insert = insert.Trim(',') + " )";
  return new[] {create, insert};
}

(Yes, yes, I know I should have learned from my last post and used a StringBuilder here as I pointed out in my last post, but seriously, this method will only ever be called once)

Now when it is called it will create the correct table with all the columns I need. A couple of example mappings for the database in FluentNH are shown below:

public InvestSpecMap() {
  WithTable("InvestSpec");
  Id(x => x.Id).ColumnName("InvestSpecID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestSpec"); //ID counter column name

public PriceMap() {
  WithTable("InvestPrice");
  Id(x => x.Id).ColumnName("InvestPriceID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestPrice"); //ID counter column name

To be completely "clean code" and avoid repeating myself I should probably factor out the Id() code into a method in an inhereted base class so I can call it from each mapping class like this:

protected void SetIdGenerator(string tablename) {
  Id(x => x.Id).ColumnName(TableName + "Id")
    .SetGeneratorClass(typeof(FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", AllColumns)
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", TableName); //ID counter column name
}

Now I can unit test using a temporary in-memory SQLite database and all my tests are passing.

Creating a custom id generator for nHibernate

Chris Nicola — Thu, 03 Sep 2009 16:41:21 GMT

Revision 1 posted to How to by Chris Nicola on 03/09/2009 01:41:21 p.m.

Part 1: Inheriting from TableGenerator class

It isn't complex, but it also isn't one of the identity strategies available in nHibernate and I fully intend to use nHibernate.

One of the beautiful things about nHibernate the ability to extend it. You can extend its functionality without ever touching their source code.

It was very easy to locate the classes responsible for ID generation in the NHibernate.ID namespace. It was also clear immediately that most classes inherited from IIdentifierGenerator. I also knew that my strategy was similar to the procedure that hilo implements so I started with TableHiLoGenerator which inherts from TableGenerator.

public class FDPSequence : TableGenerator
{
    private const Int32 SeedValue = 1048576;
 
    private static readonly ILog Log = LogManager.GetLogger(typeof(FDPSequence));
 
    public override object Generate(ISessionImplementor session, object obj)
    {
        int counter = Convert.ToInt32(base.Generate(session, obj));
        return counter + SeedValue + 1;
    }
}

In order to use this custom generator class I setup my configuration to use it. Using Fluent I wrote a mapping like this:

public class InvestSpecMap : FDPEntityBaseMap<InvestSpec>
{
    public InvestSpecMap()
    {
        WithTable("InvestSpec");
        Id(x => x.Id).ColumnName(tablename + "ID")
            .SetGeneratorClass(typeof(FDPGenerator.FDPSequence).AssemblyQualifiedName)
            .AddGeneratorParam("table", "zSysCounters") //Name of the ID counter table
            .AddGeneratorParam("column", "InvestSpec"); //ID counter column for this table
        Map(x => x.AnnualDividend).ColumnName("AnnlzdDiv");
        Map(x => x.AssetClass);
        Map(x => x.CurrencyType);
        Map(x => x.CusipNumber).ColumnName("CusipNum");
        Map(x => x.DividendFreq).ColumnName("DivFrequency");
        Map(x => x.FullName);
        Map(x => x.MaturityDate).ColumnName("MaturityDt");
        Map(x => x.PriceAsOf).ColumnName("PriceAsOfDt");
        Map(x => x.ShortName).ColumnName("AbbrName");
        Map(x => x.TaxTreatment);
        Map(x => x.TickerSymbol);
        Map(x => x.Type);
        Map(x => x.UnitPrice);
    }
}

You can do the same with XML mappings just declare the assembly and class as you usually would in XML. This is actually the first time I've used FluentNH.

Part 2: Stealing from TableGenerator and controlling DDL generation

public string[] SqlCreateStrings(Dialect dialect) {
  string create = "create table " + tableName + " (";
  string insert = "insert into " + tableName + " values (";
  foreach (string s in allcolumns.Split(',')) {
    create += " " + s + " " + dialect.GetTypeName(columnSqlType) + ",";
    insert += " 1,";
  }
  create = create.Trim(',') + " )";
  insert = insert.Trim(',') + " )";
  return new[] {create, insert};
}

(Yes, yes, I know I should have learned from my last post and used a StringBuilder here as I pointed out in my last post, but seriously, this method will only ever be called once)

Now when it is called it will create the correct table with all the columns I need. A couple of example mappings for the database in FluentNH are shown below:

public InvestSpecMap() {
  WithTable("InvestSpec");
  Id(x => x.Id).ColumnName("InvestSpecID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestSpec"); //ID counter column name

public PriceMap() {
  WithTable("InvestPrice");
  Id(x => x.Id).ColumnName("InvestPriceID")
    .SetGeneratorClass(typeof (FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", "InvestSpec, InvestPrice")
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", "InvestPrice"); //ID counter column name

To be completely "clean code" and avoid repeating myself I should probably factor out the Id() code into a method in an inhereted base class so I can call it from each mapping class like this:

protected void SetIdGenerator(string tablename) {
  Id(x => x.Id).ColumnName(TableName + "Id")
    .SetGeneratorClass(typeof(FdpSequenceGen).AssemblyQualifiedName)
    .AddGeneratorParam("allcolumns", AllColumns)
    .AddGeneratorParam("table", "zSysCounters") //ID counter table name
    .AddGeneratorParam("column", TableName); //ID counter column name
}

Now I can unit test using a temporary in-memory SQLite database and all my tests are passing.

Checking if an Unloaded Collection Contains Elements

Ricardo Peres — Fri, 18 Nov 2011 15:35:52 GMT

Current revision posted to How to by Ricardo Peres on 18/11/2011 12:35:52 p.m.

If you want to know if an unloaded collection in an entity contains elements, or count them, without actually loading them, you need to use a custom query; that is because the Count property (if the collection is not mapped with lazy=”extra”) and the LINQ Count() andAny() methods force the whole collection to be loaded.

You can use something like these two methods, one for checking if there are any values, the other for actually counting them:

public static Boolean Exists(this ISession session, IEnumerable collection)

     if (collection is IPersistentCollection)

         IPersistentCollection col = collection as IPersistentCollection;

         if (col.WasInitialized == false)

                 String[] roleParts = col.Role.Split('.');

                 String ownerTypeName = String.Join(".", roleParts, 0, roleParts.Length - 1);

                 String ownerCollectionName = roleParts.Last();

                 String hql = "select 1 from " + ownerTypeName + " it where it.id = :id and exists elements(it." + ownerCollectionName + ")";

                 Boolean exists = session.CreateQuery(hql).SetParameter("id", col.Key).List().Count == 1;

                 return (exists);

     return ((collection as IEnumerable).OfType<Object>().Any());

public static Int64 Count(this ISession session, IEnumerable collection)

    if (collection is IPersistentCollection)

        IPersistentCollection col = collection as IPersistentCollection;

        if (col.WasInitialized == false)

            String[] roleParts = col.Role.Split('.');

            String ownerTypeName = String.Join(".", roleParts, 0, roleParts.Length - 1);

            String ownerCollectionName = roleParts.Last();

            String hql = "select count(elements(it." + ownerCollectionName + ")) from " + ownerTypeName + " it where it.id = :id";

            Int64 count = session.CreateQuery(hql).SetParameter("id", col.Key).UniqueResult<Int64>();

            return (count);

    return ((collection as IEnumerable).OfType<Object>().Count());

Here's how:

MyEntity entity = session.Load(100);

if (session.Exists(entity.SomeCollection))

    Int32 count = session.Count(entity.SomeCollection);

    //...

Localization techniques

brendan2452 — Sat, 29 Oct 2011 01:07:45 GMT

Current revision posted to How to by brendan2452 on 28/10/2011 10:07:45 p.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.

It is based on implementing IUserType, providing methods to serialize and deserialize the property. This way, we make use of NHibernate extensibility to provide a seamless mechanism to store and retrieve the property in a field of the database.

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

Alternatively, you can create your our own class to contain all the translations and ease the addition and removal of them as well as properties to have quick access to the current localization string based on Thread.CurrentThread.CurrentCulture. In some of the proposals in the second method discussed there are examples of such classes that can be easily adapted to this method. This, as well, can be exposed as a string through the proper getter.

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

This is an interesting approach, quite simple in explanation but uses a couple of advanced NHibernate features such as formulas and filters. The advantage is that the property of the entity is a simple string and the selection of the language to load is made through the formula based on a session parameter.

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

This one uses a nice crafted class to store and retrieve localization information and a couple of tables, one containing the dictionaries that create the relationship between the entity and the translations, that are accessed via a <map> in the mapping. (NOTE: I have not tested it, and he says that you can map several properties in the same entity with this method but not with the provided mapping)

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The method proposed here is very similar to the former one, in this case using three tables, but that's up to you. It explains how to do the mapping using an Id different from the PK (which can't be done at this moment using Fluent NHibernate, just in case you want to).

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

A very thorough example. It maps only one property per entity, simplifying the mappings and the table structure and can be more than enough for many solutions. It discusses a lot about a Registry object to hold the current locale, but you can change that to rely in Thread.CurrentThread.CurrentCulture and simplify a little bit.

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the [[howtonh:stuffynoseremedy.net/stuffy-nose-remedy/|stuffy nose remedy]] mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

John Davidson — Fri, 28 Oct 2011 14:13:21 GMT

Revision 13 posted to How to by John Davidson on 28/10/2011 11:13:21 a.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

liliasmit — Fri, 28 Oct 2011 13:56:54 GMT

Revision 12 posted to How to by liliasmit on 28/10/2011 10:56:54 a.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

John Davidson — Wed, 06 Jul 2011 13:22:53 GMT

Revision 11 posted to How to by John Davidson on 06/07/2011 10:22:53 a.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

ThisMBA Project reports second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

MBA Project reports — Wed, 06 Jul 2011 04:59:56 GMT

Revision 10 posted to How to by MBA Project reports on 06/07/2011 01:59:56 a.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

This MBA Project reports second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

John Davidson — Fri, 01 Jul 2011 10:41:47 GMT

Revision 9 posted to How to by John Davidson on 01/07/2011 07:41:47 a.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search DUI Lawyer in huntington Beach and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

John Davidson — Fri, 01 Jul 2011 10:41:12 GMT

Revision 8 posted to How to by John Davidson on 01/07/2011 07:41:12 a.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.Mustuniversity | Must University

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

LCD HDTV

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

Criminal Defense Lawyer in Long Beach — Fri, 01 Jul 2011 07:43:11 GMT

Revision 7 posted to How to by Criminal Defense Lawyer in Long Beach on 01/07/2011 04:43:11 a.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

LCD HDTV

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

markweee — Wed, 30 Mar 2011 11:47:46 GMT

Revision 6 posted to How to by markweee on 30/03/2011 08:47:46 a.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

LCD HDTV

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

mikeon098 — Fri, 24 Sep 2010 17:18:41 GMT

Revision 5 posted to How to by mikeon098 on 24/09/2010 02:18:41 p.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

LCD HDTV

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

tcook23 — Thu, 26 Aug 2010 12:35:37 GMT

Revision 4 posted to How to by tcook23 on 26/08/2010 09:35:37 a.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

LCD HDTV

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

mike3050 — Fri, 28 May 2010 12:41:41 GMT

Revision 3 posted to How to by mike3050 on 28/05/2010 09:41:41 a.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

Marc Climent — Tue, 16 Mar 2010 15:27:42 GMT

Revision 2 posted to How to by Marc Climent on 16/03/2010 12:27:42 p.m.

Localization techniques

Filed under: IUserType, Filters, l18n, localization, property

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.

In the example, the property is a Dictionary (internally) but we choose to expose it as a String developing the getter (in Fabio's post) to make it easier for the user.

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)
The entity property can't be a string

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Localization techniques

Marc Climent — Tue, 16 Mar 2010 12:18:25 GMT

Revision 1 posted to How to by Marc Climent on 16/03/2010 09:18:25 a.m.

This page is a summary of the two main different approaches found all around the web on Property Localization using NHibernate, based on a post in spanish on my own blog.

There are roughly two main paths

Method 1: Using a custom IUserType

This method is exposed thoroughly in a Fabio Maulo`s post called Localized Property with NHibernate, in which he discusses the use of the LocalizablePropertyType found in uNhAddIns.

In the example, the property is a Dictionary but we can create our own class to contain all the translations and ease the addition and removal of them as well as properties to have quick access to the current localization string based on Thread.CurrentThread.CurrentCulture. In some of the proposals in the second method discussed there are examples of such classes that can be easily adapted to this method.

Pros:

Simple and easy
Data stored in the same table as the entity
Fairly transparent, specially if a custom object is used to simplify the access to the translations

Cons:

The value of the field is not understandable by the DBMS (no indexing, sorting or whatever)
The entity property can't be a string

Method 2: Using several tables

This second method has many variants, but all of them use one or more tables to store the translations, making them visible to the DBMS.

Proposal 2.1: Localizing NHibernate: Contextual Parameters by Ayende

Proposal 2.2: Create a multi languaged domain model with NHibernate and C# by Michal @ WebDevBros

The class called PhraseDictionary can be easily used through a IUserType with the first method.

Proposal 2.3: Mapping translations in NHibernate by Siim Viikman

The PhraseDictionary has been replaced by the Translation class, but essentially are the same, holders of the translation dictionary. Can be adapted as well to use it with method 1.

Proposal 2.4: Localizable entities with Nhibernate part 1 (part 2 and part 3) by Alkampfer

Pros:

DBMS-aware solution

Cons:

More complex mappings
More complex data structure

Conclusions

Localization is painful in most scenarios and some guidelines can be followed:

If you don't really need that a property is localizable, don't make it localizable. Ok, in most cases is not your decision. If you have choice, think it twice or thrice before making a property localizable.
If you don't need to use DBMS capabilities on the field (such as sorting), go for the first method, it's easy to to the IUserType and the mappings and as well as the serialization is well tested won't give much trouble
If you need DBMS capabilities, in most cases only some properties will need this, so instead of embracing blindly the second method, think if a mixed solution is not simpler and better for you. (Was in my case)

As a side note, if you need to index the property, think of using NHibernate.Search and Lucene.NET using method 1 and a custom Bridge implementation to store the localizations in the index.

Finally, thanks to all that participated in NHUsers discussion on the topic.

Configure Log4Net for use with NHibernate

John Davidson — Mon, 19 Sep 2011 21:52:01 GMT

Current revision posted to How to by John Davidson on 19/09/2011 06:52:01 p.m.

Configure Log4Net for use with NHibernate

Filed under: logging, log4net

The Log4Net assembly is distributed with NHibernate binaries.

If you are not sure about details of the configuration shown below please refer to this documentation.

Running without Log4Net

If you only want NHibernate to log the queries it sends to the data source when running unit tests you don't have to configure Log4Net at all. It suffices to add the show_sql key to the NHibernate configuration. If you are using a separate xml file to configure NHibernate (e.g. the hibernate.cfg.xml) then its content might look similar to the one below

I am not too lazy to write an academic paper. I just do not have time for writing. Thus, I need to go to the essay writing service to get custom papers, which are composed by the best writing experts. I understand that a lot of people cannot become successful without writing assistance.

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
  <session-factory>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
  <property name="dialect">NHibernate.Dialect.MsSql2005Dialect</property>
  <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
  <property name="connection.connection_string">
    Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;
  </property>
  <property name="show_sql">true</property>
  </session-factory>
</hibernate-configuration>

Now when running any unit test that involves NHibernate the queries generated by NHibernate will be logged in the output window (be it the unit test runner of Resharper or be it the Output Window of Visual Studio when you useTestDriven).

Logging with Log4Net

If you want to use Log4Net to collect logging information generated by NHibernate you have to add the necessary configuration to the config file of your application. If you want to log to two different targets (e.g. to the console and to a file) the relevant sections in your config file might look like followsThesis Writing AND Dissertation Writing AND Essay Writing:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <!-- Others sections -->
    <section name="log4net"
      type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
  </configSections>

  <!-- Some others configurations -->

  <!-- This section contains the log4net configuration settings -->
  <log4net debug="false">

    <!-- Define some output appenders -->
    <appender name="trace"
          type="log4net.Appender.TraceAppender, log4net">
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
             value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
      </layout>
    </appender>

    <appender name="console"
          type="log4net.Appender.ConsoleAppender, log4net">
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
             value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
      </layout>
    </appender>

    <appender name="rollingFile"
          type="log4net.Appender.RollingFileAppender,log4net" >

      <param name="File" value="log.txt" />
      <param name="AppendToFile" value="false" />
      <param name="RollingStyle" value="Date" />
      <param name="DatePattern" value="yyyy.MM.dd" />
      <param name="StaticLogFileName" value="true" />

      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
          value="%d [%t] %-5p %c - %m%n" />
      </layout>
    </appender>

    <!-- Setup the root category, add the appenders and set the default priority -->
    <root>
      <priority value="DEBUG" />
      <appender-ref ref="console" />
    </root>

  </log4net>
</configuration>

Here I define that all output with a priority of at least DEBUG goes to the console.

Now I have to tell my application that I want to use Log4Net. I can do that with an assembly level attribute. That is, you have to put the following code snippet somewhere in your application (e.g. the "Global. asax" if you are building a web application)

// Configure log4net using the .config file
[assembly: log4net.Config.XmlConfigurator(Watch = true)]

having done do we can now run a first unit test that accesses the database via NHibernate. The output generated by Log4Net in the unit test runner is similar to this

2008-07-02 08:40:07,249 INFO NHibernate 2.0.0.4000 (2.0.0.4000)
2008-07-02 08:40:07,251 INFO hibernate-configuration section not found in application configuration file
2008-07-02 08:40:07,254 INFO Bytecode provider name : lcg
2008-07-02 08:40:07,257 INFO Using reflection optimizer
2008-07-02 08:40:08,515 DEBUG connection.provider=NHibernate.Connection.DriverConnectionProvider
2008-07-02 08:40:08,516 DEBUG dialect=NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:08,517 DEBUG connection.driver_class=NHibernate.Driver.SqlClientDriver
2008-07-02 08:40:08,517 DEBUG connection.connection_string=Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;
2008-07-02 08:40:08,518 DEBUG show_sql=false
2008-07-02 08:40:08,522 DEBUG properties: System.Collections.Generic.Dictionary`2[System.String,System.String]
2008-07-02 08:40:08,526 INFO Mapping resource: LoggingSample.Person.hbm.xml
2008-07-02 08:40:08,872 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:11,425 INFO Mapping class: LoggingSample.Person -> Person
2008-07-02 08:40:11,537 DEBUG Mapped property: Id -> Id, type: Int32
2008-07-02 08:40:11,612 DEBUG Mapped property: LastName -> LastName, type: String
2008-07-02 08:40:11,614 DEBUG Mapped property: FirstName -> FirstName, type: String
2008-07-02 08:40:11,614 DEBUG Mapped property: Birthdate -> Birthdate, type: DateTime
2008-07-02 08:40:11,632 INFO checking mappings queue
2008-07-02 08:40:11,634 INFO processing one-to-many association mappings
2008-07-02 08:40:11,634 INFO processing one-to-one association property references
2008-07-02 08:40:11,634 INFO processing foreign key constraints
2008-07-02 08:40:11,712 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:11,716 INFO Using dialect defined converter
...
2008-07-02 08:40:12,410 DEBUG Static SQL for entity: LoggingSample.Person
2008-07-02 08:40:12,411 DEBUG  Version select: SELECT Id FROM Person WHERE Id = ?
2008-07-02 08:40:12,412 DEBUG  Snapshot select: SELECT person_.Id, person_.LastName as LastName0_, person_.FirstName as FirstName0_, person_.Birthdate as Birthdate0_ FROM Person person_ WHERE person_.Id=?
...

as you can see LOADS of information.

To tune the generated logging information a little bit we can filter the output generated by NHibernate by putting the following configuration section into our config file (put them just after the root section inside the log4net node)

    <logger name="NHibernate">
      <level value="WARN" />
    </logger>

    <logger name="NHibernate.SQL">
      <level value="DEBUG" />
    </logger>

Obviously NHibernate defines two different loggers NHibernate and NHibernate.SQL. The first one receives all logging output that NHibernate generates where as the second one only receives the sql statements generated by NHibernate.

With the above settings in place the output generated is reduced to

2008-07-02 08:48:58,636 DEBUG select person0_.Id as Id0_, 
                        person0_.LastName as LastName0_, 
                        person0_.FirstName as FirstName0_, 
                        person0_.Birthdate as Birthdate0_ 
                        from Person person0_

That's what we want. Only if we have some weird problems we need to change the priority level of the NHibernate filter to say INFO or DEBUG.

Configure Log4Net for use with NHibernate

barbarasmith22 — Mon, 19 Sep 2011 11:10:23 GMT

Revision 5 posted to How to by barbarasmith22 on 19/09/2011 08:10:23 a.m.

Configure Log4Net for use with NHibernate

Filed under: logging, log4net

The Log4Net assembly is distributed with NHibernate binaries.

If you are not sure about details of the configuration shown below please refer to this documentation.

Running without Log4Net

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
  <session-factory>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
  <property name="dialect">NHibernate.Dialect.MsSql2005Dialect</property>
  <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
  <property name="connection.connection_string">
    Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;
  </property>
  <property name="show_sql">true</property>
  </session-factory>
</hibernate-configuration>

Logging with Log4Net

If you want to use Log4Net to collect logging information generated by NHibernate you have to add the necessary configuration to the config file of your application. If you want to log to two different targets (e.g. to the console and to a file) the relevant sections in your config file might look like follows Thesis Writing AND Dissertation Writing AND Essay Writing

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <!-- Others sections -->
    <section name="log4net"
      type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
  </configSections>

  <!-- Some others configurations -->

  <!-- This section contains the log4net configuration settings -->
  <log4net debug="false">

    <!-- Define some output appenders -->
    <appender name="trace"
          type="log4net.Appender.TraceAppender, log4net">
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
             value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
      </layout>
    </appender>

    <appender name="console"
          type="log4net.Appender.ConsoleAppender, log4net">
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
             value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
      </layout>
    </appender>

    <appender name="rollingFile"
          type="log4net.Appender.RollingFileAppender,log4net" >

      <param name="File" value="log.txt" />
      <param name="AppendToFile" value="false" />
      <param name="RollingStyle" value="Date" />
      <param name="DatePattern" value="yyyy.MM.dd" />
      <param name="StaticLogFileName" value="true" />

      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
          value="%d [%t] %-5p %c - %m%n" />
      </layout>
    </appender>

    <!-- Setup the root category, add the appenders and set the default priority -->
    <root>
      <priority value="DEBUG" />
      <appender-ref ref="console" />
    </root>

  </log4net>
</configuration>

Here I define that all output with a priority of at least DEBUG goes to the console.

// Configure log4net using the .config file
[assembly: log4net.Config.XmlConfigurator(Watch = true)]

having done do we can now run a first unit test that accesses the database via NHibernate. The output generated by Log4Net in the unit test runner is similar to this

2008-07-02 08:40:07,249 INFO NHibernate 2.0.0.4000 (2.0.0.4000)
2008-07-02 08:40:07,251 INFO hibernate-configuration section not found in application configuration file
2008-07-02 08:40:07,254 INFO Bytecode provider name : lcg
2008-07-02 08:40:07,257 INFO Using reflection optimizer
2008-07-02 08:40:08,515 DEBUG connection.provider=NHibernate.Connection.DriverConnectionProvider
2008-07-02 08:40:08,516 DEBUG dialect=NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:08,517 DEBUG connection.driver_class=NHibernate.Driver.SqlClientDriver
2008-07-02 08:40:08,517 DEBUG connection.connection_string=Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;
2008-07-02 08:40:08,518 DEBUG show_sql=false
2008-07-02 08:40:08,522 DEBUG properties: System.Collections.Generic.Dictionary`2[System.String,System.String]
2008-07-02 08:40:08,526 INFO Mapping resource: LoggingSample.Person.hbm.xml
2008-07-02 08:40:08,872 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:11,425 INFO Mapping class: LoggingSample.Person -> Person
2008-07-02 08:40:11,537 DEBUG Mapped property: Id -> Id, type: Int32
2008-07-02 08:40:11,612 DEBUG Mapped property: LastName -> LastName, type: String
2008-07-02 08:40:11,614 DEBUG Mapped property: FirstName -> FirstName, type: String
2008-07-02 08:40:11,614 DEBUG Mapped property: Birthdate -> Birthdate, type: DateTime
2008-07-02 08:40:11,632 INFO checking mappings queue
2008-07-02 08:40:11,634 INFO processing one-to-many association mappings
2008-07-02 08:40:11,634 INFO processing one-to-one association property references
2008-07-02 08:40:11,634 INFO processing foreign key constraints
2008-07-02 08:40:11,712 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:11,716 INFO Using dialect defined converter
...
2008-07-02 08:40:12,410 DEBUG Static SQL for entity: LoggingSample.Person
2008-07-02 08:40:12,411 DEBUG  Version select: SELECT Id FROM Person WHERE Id = ?
2008-07-02 08:40:12,412 DEBUG  Snapshot select: SELECT person_.Id, person_.LastName as LastName0_, person_.FirstName as FirstName0_, person_.Birthdate as Birthdate0_ FROM Person person_ WHERE person_.Id=?
...

as you can see LOADS of information.

    <logger name="NHibernate">
      <level value="WARN" />
    </logger>

    <logger name="NHibernate.SQL">
      <level value="DEBUG" />
    </logger>

With the above settings in place the output generated is reduced to

2008-07-02 08:48:58,636 DEBUG select person0_.Id as Id0_, 
                        person0_.LastName as LastName0_, 
                        person0_.FirstName as FirstName0_, 
                        person0_.Birthdate as Birthdate0_ 
                        from Person person0_

That's what we want. Only if we have some weird problems we need to change the priority level of the NHibernate filter to say INFO or DEBUG.

Configure Log4Net for use with NHibernate

markweee — Wed, 30 Mar 2011 11:21:17 GMT

Revision 4 posted to How to by markweee on 30/03/2011 08:21:17 a.m.

Configure Log4Net for use with NHibernate

Filed under: logging, log4net

The Log4Net assembly is distributed with NHibernate binaries.

If you are not sure about details of the configuration shown below please refer to this documentation.

Running without Log4Net

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
  <session-factory>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
  <property name="dialect">NHibernate.Dialect.MsSql2005Dialect</property>
  <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
  <property name="connection.connection_string">
    Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;
  </property>
  <property name="show_sql">true</property>
  </session-factory>
</hibernate-configuration>

Logging with Log4Net

If you want to use Log4Net to collect logging information generated by NHibernate you have to add the necessary configuration to the config file of your application. If you want to log to two different targets (e.g. to the console and to a file) the relevant sections in your config file might look like follows Thesis Writing AND Dissertation Writing AND Essay Writing

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <!-- Others sections -->
    <section name="log4net"
      type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
  </configSections>

  <!-- Some others configurations -->

  <!-- This section contains the log4net configuration settings -->
  <log4net debug="false">

    <!-- Define some output appenders -->
    <appender name="trace"
          type="log4net.Appender.TraceAppender, log4net">
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
             value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
      </layout>
    </appender>

    <appender name="console"
          type="log4net.Appender.ConsoleAppender, log4net">
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
             value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
      </layout>
    </appender>

    <appender name="rollingFile"
          type="log4net.Appender.RollingFileAppender,log4net" >

      <param name="File" value="log.txt" />
      <param name="AppendToFile" value="false" />
      <param name="RollingStyle" value="Date" />
      <param name="DatePattern" value="yyyy.MM.dd" />
      <param name="StaticLogFileName" value="true" />

      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
          value="%d [%t] %-5p %c - %m%n" />
      </layout>
    </appender>

    <!-- Setup the root category, add the appenders and set the default priority -->
    <root>
      <priority value="DEBUG" />
      <appender-ref ref="console" />
    </root>

  </log4net>
</configuration>

Here I define that all output with a priority of at least DEBUG goes to the console.

// Configure log4net using the .config file
[assembly: log4net.Config.XmlConfigurator(Watch = true)]

having done do we can now run a first unit test that accesses the database via NHibernate. The output generated by Log4Net in the unit test runner is similar to this

2008-07-02 08:40:07,249 INFO NHibernate 2.0.0.4000 (2.0.0.4000)
2008-07-02 08:40:07,251 INFO hibernate-configuration section not found in application configuration file
2008-07-02 08:40:07,254 INFO Bytecode provider name : lcg
2008-07-02 08:40:07,257 INFO Using reflection optimizer
2008-07-02 08:40:08,515 DEBUG connection.provider=NHibernate.Connection.DriverConnectionProvider
2008-07-02 08:40:08,516 DEBUG dialect=NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:08,517 DEBUG connection.driver_class=NHibernate.Driver.SqlClientDriver
2008-07-02 08:40:08,517 DEBUG connection.connection_string=Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;
2008-07-02 08:40:08,518 DEBUG show_sql=false
2008-07-02 08:40:08,522 DEBUG properties: System.Collections.Generic.Dictionary`2[System.String,System.String]
2008-07-02 08:40:08,526 INFO Mapping resource: LoggingSample.Person.hbm.xml
2008-07-02 08:40:08,872 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:11,425 INFO Mapping class: LoggingSample.Person -> Person
2008-07-02 08:40:11,537 DEBUG Mapped property: Id -> Id, type: Int32
2008-07-02 08:40:11,612 DEBUG Mapped property: LastName -> LastName, type: String
2008-07-02 08:40:11,614 DEBUG Mapped property: FirstName -> FirstName, type: String
2008-07-02 08:40:11,614 DEBUG Mapped property: Birthdate -> Birthdate, type: DateTime
2008-07-02 08:40:11,632 INFO checking mappings queue
2008-07-02 08:40:11,634 INFO processing one-to-many association mappings
2008-07-02 08:40:11,634 INFO processing one-to-one association property references
2008-07-02 08:40:11,634 INFO processing foreign key constraints
2008-07-02 08:40:11,712 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:11,716 INFO Using dialect defined converter
...
2008-07-02 08:40:12,410 DEBUG Static SQL for entity: LoggingSample.Person
2008-07-02 08:40:12,411 DEBUG  Version select: SELECT Id FROM Person WHERE Id = ?
2008-07-02 08:40:12,412 DEBUG  Snapshot select: SELECT person_.Id, person_.LastName as LastName0_, person_.FirstName as FirstName0_, person_.Birthdate as Birthdate0_ FROM Person person_ WHERE person_.Id=?
...

as you can see LOADS of information.

    <logger name="NHibernate">
      <level value="WARN" />
    </logger>

    <logger name="NHibernate.SQL">
      <level value="DEBUG" />
    </logger>

With the above settings in place the output generated is reduced to

2008-07-02 08:48:58,636 DEBUG select person0_.Id as Id0_, 
                        person0_.LastName as LastName0_, 
                        person0_.FirstName as FirstName0_, 
                        person0_.Birthdate as Birthdate0_ 
                        from Person person0_

That's what we want. Only if we have some weird problems we need to change the priority level of the NHibernate filter to say INFO or DEBUG.

Configure Log4Net for use with NHibernate

Dario Quintana — Fri, 17 Oct 2008 00:23:49 GMT

Revision 3 posted to How to by Dario Quintana on 16/10/2008 09:23:49 p.m.

Configure Log4Net for use with NHibernate

Filed under: logging, log4net

The Log4Net assebly assembly is distributed with NHibernate binaries.

If you are not sure about details of the configuration shown below please refer to this documentation.

Running without Log4Net

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
  <session-factory>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
  <property name="dialect">NHibernate.Dialect.MsSql2005Dialect</property>
  <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
  <property name="connection.connection_string">
    Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;
  </property>
  <property name="show_sql">true</property>
  </session-factory>
</hibernate-configuration>

Logging with Log4Net

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <!-- Others sections -->
    <section name="log4net"
      type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
  </configSections>

  <!-- Some others configurations -->

  <!-- This section contains the log4net configuration settings -->
  <log4net debug="false">

    <!-- Define some output appenders -->
    <appender name="trace"
          type="log4net.Appender.TraceAppender, log4net">
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
             value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
      </layout>
    </appender>

    <appender name="console"
          type="log4net.Appender.ConsoleAppender, log4net">
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
             value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
      </layout>
    </appender>

    <appender name="rollingFile"
          type="log4net.Appender.RollingFileAppender,log4net" >

      <param name="File" value="log.txt" />
      <param name="AppendToFile" value="false" />
      <param name="RollingStyle" value="Date" />
      <param name="DatePattern" value="yyyy.MM.dd" />
      <param name="StaticLogFileName" value="true" />

      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
          value="%d [%t] %-5p %c - %m%n" />
      </layout>
    </appender>

    <!-- Setup the root category, add the appenders and set the default priority -->
    <root>
      <priority value="DEBUG" />
      <appender-ref ref="console" />
    </root>

  </log4net>
</configuration>

Here I define that all output with a priority of at least DEBUG goes to the console.

// Configure log4net using the .config file
[assembly: log4net.Config.XmlConfigurator(Watch = true)]

having done do we can now run a first unit test that accesses the database via NHibernate. The output generated by Log4Net in the unit test runner is similar to this

2008-07-02 08:40:07,249 INFO NHibernate 2.0.0.4000 (2.0.0.4000)
2008-07-02 08:40:07,251 INFO hibernate-configuration section not found in application configuration file
2008-07-02 08:40:07,254 INFO Bytecode provider name : lcg
2008-07-02 08:40:07,257 INFO Using reflection optimizer
2008-07-02 08:40:08,515 DEBUG connection.provider=NHibernate.Connection.DriverConnectionProvider
2008-07-02 08:40:08,516 DEBUG dialect=NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:08,517 DEBUG connection.driver_class=NHibernate.Driver.SqlClientDriver
2008-07-02 08:40:08,517 DEBUG connection.connection_string=Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;
2008-07-02 08:40:08,518 DEBUG show_sql=false
2008-07-02 08:40:08,522 DEBUG properties: System.Collections.Generic.Dictionary`2[System.String,System.String]
2008-07-02 08:40:08,526 INFO Mapping resource: LoggingSample.Person.hbm.xml
2008-07-02 08:40:08,872 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:11,425 INFO Mapping class: LoggingSample.Person -> Person
2008-07-02 08:40:11,537 DEBUG Mapped property: Id -> Id, type: Int32
2008-07-02 08:40:11,612 DEBUG Mapped property: LastName -> LastName, type: String
2008-07-02 08:40:11,614 DEBUG Mapped property: FirstName -> FirstName, type: String
2008-07-02 08:40:11,614 DEBUG Mapped property: Birthdate -> Birthdate, type: DateTime
2008-07-02 08:40:11,632 INFO checking mappings queue
2008-07-02 08:40:11,634 INFO processing one-to-many association mappings
2008-07-02 08:40:11,634 INFO processing one-to-one association property references
2008-07-02 08:40:11,634 INFO processing foreign key constraints
2008-07-02 08:40:11,712 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:11,716 INFO Using dialect defined converter
...
2008-07-02 08:40:12,410 DEBUG Static SQL for entity: LoggingSample.Person
2008-07-02 08:40:12,411 DEBUG  Version select: SELECT Id FROM Person WHERE Id = ?
2008-07-02 08:40:12,412 DEBUG  Snapshot select: SELECT person_.Id, person_.LastName as LastName0_, person_.FirstName as FirstName0_, person_.Birthdate as Birthdate0_ FROM Person person_ WHERE person_.Id=?
...

as you can see LOADS of information.

    <logger name="NHibernate">
      <level value="WARN" />
    </logger>

    <logger name="NHibernate.SQL">
      <level value="DEBUG" />
    </logger>

With the above settings in place the output generated is reduced to

2008-07-02 08:48:58,636 DEBUG select person0_.Id as Id0_, 
                        person0_.LastName as LastName0_, 
                        person0_.FirstName as FirstName0_, 
                        person0_.Birthdate as Birthdate0_ 
                        from Person person0_

That's what we want. Only if we have some weird problems we need to change the priority level of the NHibernate filter to say INFO or DEBUG.

Configure Log4Net for use with NHibernate

Fabio Maulo — Sun, 07 Sep 2008 17:20:36 GMT

Revision 2 posted to How to by Fabio Maulo on 07/09/2008 02:20:36 p.m.

Configure Log4Net for use with NHibernate

Recently there was a question in the NHUser group about how to configure

The Log4Net to log the queries generated by assebly is distributed with NHibernate . First of all: you can get Log4Net here. There you also find the documentationbinaries.

If you are not sure about details of the configuration shown below please refer to this documentation.

Running without Log4Net

<?xml  version=version="1.0"  encoding=encoding="utf-8" ?><o:p></o:p>
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2"><o:p></o:p>"urn:nhibernate-configuration-2.2">
  <session-factory><o:p></o:p>
    <property name="connection.provider">"connection.provider">NHibernate.Connection.DriverConnectionProvider</property><o:p></o:p>
  <property name="dialect">"dialect">NHibernate.Dialect.MsSql2005Dialect</property><o:p></o:p>
  <property name="connection.driver_class">"connection.driver_class">NHibernate.Driver.SqlClientDriver</property><o:p></o:p>
  <property name="connection.connection_string">"connection.connection_string">
    Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;
  </property>   >
  <property name="show_sql">"show_sql">true</property><o:p></o:p>
  </session-factory><o:p></o:p>
</hibernate-configuration><o:p></o:p>

Logging with Log4Net

...

<section name=

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <!-- Others sections -->
    <section name="log4net"type=
      type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
  </configSections>
 
  <log4net>
    <appender name="ConsoleAppender" type="log4net.Appender.ConsoleAppender,

  </configSections>

  <!-- Some others configurations -->

  <!-- This section contains the log4net ">
     
<layout type="log4net.Layout.PatternLayout,
configuration settings -->
  <log4net ">
       
<param name=debug="false">

    <!-- Define some output appenders -->
    <appender name="trace"
          type="log4net.Appender.TraceAppender, log4net">
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"value="%d

             value="%d{ABSOLUTE} %p -5p %c{1}:%L - %m%n" />
     
</layout>
    </appender>
 
    <appender name="RollingFile" type=
      </layout>
    </appender>

    <appender name="console"
          type="log4net.Appender.ConsoleAppender, log4net">
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
             value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
      </layout>
    </appender>

    <appender name="rollingFile"
          type="log4net.Appender.RollingFileAppender,log4net" >
     
<param name=

      <param name="File"value= value="log.txt" />
     
<param name=
      <param name="AppendToFile"value="true"  value="false" />
     
<param name=
      <param name="RollingStyle" value="Date" />
      <param name="DatePattern"value= value="yyyy.MM.dd" />
 
     
<layout type="log4net.Layout.PatternLayout,log4net">
       
<conversionPattern value=
      <param name="StaticLogFileName" value="true" />

      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
          value="%d [%t] %p -5p %c - %m%n" />
     
</layout>
    </appender>
 
    <root>
     
<priority value=
      </layout>
    </appender>

    <!-- Setup the root category, add the appenders and set the default priority -->
    <root>
      <priority value="DEBUG" />
     
<appender-ref ref="ConsoleAppender" 
      <appender-ref ref="console" />
    </root>
   
...
</configuration>
    </root>

  </log4net>
</configuration>

Here I define that all output with a priority of at least DEBUG goes to the console.

// Configure log4net using the .config file
[assembly: log4net.Config.XmlConfigurator(Watch = true)true)]

having done do we can now run a first unit test that accesses the database via NHibernate. The output generated by Log4Net in the unit test runner is similar to this

2008-07-02 08:40:07,249 INFO NHibernate 2.0.0.1001 2.0.0.4000 (2.0.0.1001)2.0.0.4000)
2008-07-02 08:40:07,251 INFO hibernate-configuration section not found in application configuration file
2008-07-02 08:40:07,254 INFO Bytecode provider name : lcg
2008-07-02 08:40:07,257 INFO Using reflection optimizer
2008-07-02 08:40:08,515 DEBUG connection.provider=NHibernate.Connection.DriverConnectionProvider
2008-07-02 08:40:08,516 DEBUG dialect=NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:08,517 DEBUG connection.driver_class=NHibernate.Driver.SqlClientDriver
2008-07-02 08:40:08,517 DEBUG connection.connection_string=Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;
2008-07-02 08:40:08,518 DEBUG show_sql=false
2008-07-02 08:40:08,522 DEBUG properties: System.Collections.Generic.Dictionary`2[System.String,System.String]
2008-07-02 08:40:08,526 INFO Mapping resource: LoggingSample.Person.hbm.xml
2008-07-02 08:40:08,872 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:11,425 INFO Mapping class: LoggingSample.Person -> Person
2008-07-02 08:40:11,537 DEBUG Mapped property: Id -> Id, type: Int32
2008-07-02 08:40:11,612 DEBUG Mapped property: LastName -> LastName, type: String
2008-07-02 08:40:11,614 DEBUG Mapped property: FirstName -> FirstName, type: String
2008-07-02 08:40:11,614 DEBUG Mapped property: Birthdate -> Birthdate, type: DateTime
2008-07-02 08:40:11,632 INFO checking mappings queue
2008-07-02 08:40:11,634 INFO processing one-to-many association mappings
2008-07-02 08:40:11,634 INFO processing one-to-one association property references
2008-07-02 08:40:11,634 INFO processing foreign key constraints
2008-07-02 08:40:11,712 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect
2008-07-02 08:40:11,716 INFO Using dialect defined converter
...
2008-07-02 08:40:12,410 DEBUG Static SQL for entity: LoggingSample.Person
2008-07-02 08:40:12,411 DEBUG  Version select: SELECT Id FROM Person WHERE Id = ?
2008-07-02 08:40:12,412 DEBUG  Snapshot select: SELECT person_.Id, person_.LastName as LastName0_, person_.FirstName as FirstName0_, person_.Birthdate as Birthdate0_ FROM Person person_ WHERE person_.Id=?
...

as you can see LOADS of information.

<logger name=

    <logger name="NHibernate"additivity="false">
  <level value="WARN"/>      
  <appender-ref ref="RollingFile" />
  <appender-ref ref="ConsoleAppender" 
      <level value="WARN" />
</logger>
 
<logger name=
    </logger>

    <logger name="NHibernate.SQL"additivity="false">
  <level value="ALL"/>      
  <appender-ref ref="RollingFile" />
  <appender-ref ref="ConsoleAppender" 
      <level value="DEBUG" />
</logger>
    </logger>

With the above settings in place the output generated is reduced to

2008-07-02 08:48:58,636 DEBUG select person0_.Id as Id0_, 
                        person0_.LastName as LastName0_, 
                        person0_.FirstName as FirstName0_, 
                        person0_.Birthdate as Birthdate0_ 
                        from Person person0_

That's what we want. Only if we have some weird problems we need to change the priority level of the NHibernate filter to say INFO or DEBUG.

As usual you can find a demo solution here.

Configure Log4Net for use with NHibernate

gabriel.schenker — Sun, 07 Sep 2008 05:09:37 GMT

Revision 1 posted to How to by gabriel.schenker on 07/09/2008 02:09:37 a.m.

Recently there was a question in the NHUser group about how to configure Log4Net to log the queries generated by NHibernate. First of all: you can get Log4Net here. There you also find the documentation. If you are not sure about details of the configuration shown below please refer to this documentation.

Running without Log4Net

<?xml version="1.0" encoding="utf-8" ?><o:p></o:p>

<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2"><o:p></o:p>

<session-factory><o:p></o:p>

<property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property><o:p></o:p>

<property name="dialect">NHibernate.Dialect.MsSql2005Dialect</property><o:p></o:p>

<property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property><o:p></o:p>

<property name="connection.connection_string">Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;</property>

</session-factory><o:p></o:p>

</hibernate-configuration><o:p></o:p>

Now when running any unit test that involves NHibernate the queries generated by NHibernate will be logged in the output window (be it the unit test runner of Resharper or be it the Output Window of Visual Studio when you useTestDriven).

Logging with Log4Net

...

</configSections>

</layout>

</appender>

</layout>

</appender>

<root>

<appender-ref ref="ConsoleAppender" />

</root>

...

</configuration>

Here I define that all output with a priority of at least DEBUG goes to the console.

// Configure log4net using the .config file

[assembly: log4net.Config.XmlConfigurator(Watch = true)]

having done do we can now run a first unit test that accesses the database via NHibernate. The output generated by Log4Net in the unit test runner is similar to this

2008-07-02 08:40:07,249 INFO NHibernate 2.0.0.1001 (2.0.0.1001)

2008-07-02 08:40:07,251 INFO hibernate-configuration section not found in application configuration file

2008-07-02 08:40:07,254 INFO Bytecode provider name : lcg

2008-07-02 08:40:07,257 INFO Using reflection optimizer

2008-07-02 08:40:08,515 DEBUG connection.provider=NHibernate.Connection.DriverConnectionProvider

2008-07-02 08:40:08,516 DEBUG dialect=NHibernate.Dialect.MsSql2005Dialect

2008-07-02 08:40:08,517 DEBUG connection.driver_class=NHibernate.Driver.SqlClientDriver

2008-07-02 08:40:08,517 DEBUG connection.connection_string=Server=(local);Database=NHibernateFAQ;Integrated Security=SSPI;

2008-07-02 08:40:08,518 DEBUG show_sql=false

2008-07-02 08:40:08,522 DEBUG properties: System.Collections.Generic.Dictionary`2[System.String,System.String]

2008-07-02 08:40:08,526 INFO Mapping resource: LoggingSample.Person.hbm.xml

2008-07-02 08:40:08,872 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect

2008-07-02 08:40:11,425 INFO Mapping class: LoggingSample.Person -> Person

2008-07-02 08:40:11,537 DEBUG Mapped property: Id -> Id, type: Int32

2008-07-02 08:40:11,612 DEBUG Mapped property: LastName -> LastName, type: String

2008-07-02 08:40:11,614 DEBUG Mapped property: FirstName -> FirstName, type: String

2008-07-02 08:40:11,614 DEBUG Mapped property: Birthdate -> Birthdate, type: DateTime

2008-07-02 08:40:11,632 INFO checking mappings queue

2008-07-02 08:40:11,634 INFO processing one-to-many association mappings

2008-07-02 08:40:11,634 INFO processing one-to-one association property references

2008-07-02 08:40:11,634 INFO processing foreign key constraints

2008-07-02 08:40:11,712 INFO Using dialect: NHibernate.Dialect.MsSql2005Dialect

2008-07-02 08:40:11,716 INFO Using dialect defined converter

...

2008-07-02 08:40:12,410 DEBUG Static SQL for entity: LoggingSample.Person

2008-07-02 08:40:12,411 DEBUG Version select: SELECT Id FROM Person WHERE Id = ?

2008-07-02 08:40:12,412 DEBUG Snapshot select: SELECT person_.Id, person_.LastName as LastName0_, person_.FirstName as FirstName0_, person_.Birthdate as Birthdate0_ FROM Person person_ WHERE person_.Id=?

...

as you can see LOADS of information.

<appender-ref ref="RollingFile" />

<appender-ref ref="ConsoleAppender" />

</logger>

<appender-ref ref="RollingFile" />

<appender-ref ref="ConsoleAppender" />

</logger>

With the above settings in place the output generated is reduced to

2008-07-02 08:48:58,636 DEBUG select person0_.Id as Id0_,

person0_.LastName as LastName0_,

person0_.FirstName as FirstName0_,

person0_.Birthdate as Birthdate0_

from Person person0_

That's what we want. Only if we have some weird problems we need to change the priority level of the NHibernate filter to say INFO or DEBUG.

As usual you can find a demo solution here.

Get unique results from joined queries

John Davidson — Thu, 08 Sep 2011 00:31:52 GMT

Current revision posted to How to by John Davidson on 07/09/2011 09:31:52 p.m.

Get unique results from joined queries

Filed under: query

Problem:

A recurring issue that new NHibernate users keep asking about, is the fact that they sometimes get duplicate results from their queries

For example, take a look at the next model:

where Comment.Name refer to the name of the person who wrote the comment.

If you'd want to issue a query on Post that joins to Comment, say "all of the posts that were commented by 'Ken Egozi'", the next hql query should do the trick:

   select  p
   from    Post p
   join    p.Comments c
   where   c.Name = 'Ken Egozi'";

So, you go ahead and

   var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   var posts = session.CreateQuery(hql)
      .List<post>();

Assuming the next data is in the DB:

  Post#1

    Comment by 'Ken Egozi'
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

  Post#2
    Comment by 'Fabio Maulo'

  Post#3
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

you'd expect the list 'posts' to include two posts: Post#1 and Post#3.
However, if you'd look into posts, you'll see that it has three entries, two entries pointing to Post#1 and one entry pointing to Post#3Buy Term Paper AND Buy Research Paper

Note that NHibernate is smart enough not to create two separate instances for Post#1, but rather a single instance will be created, and the two entries in the list will point to the same instance in memory.Buy Thesis AND Buy Dissertation AND Buy Essay

Explanation:

The said hql query (or an equivalent Criteria) is translated to the joined SELECT clause

   SELECT  {p.*}
   FROM    Posts p
     JOIN  Comments c ON c.PostId = p.Id
   WHERE   c.[Name] = 'Ken Egozi'

where {p.*} is substituted by the list of fields needed to satisfy a Post object. Running this SQL query directly on the data detailed above, will result with three lines in the resultset.

Solutions

There are three solutions to that in SQL world:

The DISTINCT keyword, when added on the fields of Posts, will ensure that there will be no duplicate lines. there are a few problems with that. Some RDBMS systems will not allow DISTINCT over certain data types, like the blob types in SQL Server. And if you also need to retrieve the joined data, then the DISTINCT keyword will be useless.

Using a subselect

   SELECT *
   FROM   Posts p
   WHERE EXISTS
   (
      SELECT 1
      FROM   Comments c
      WHERE  c.PostId = p.Id
        AND  c.[Name] = 'Ken Egozi'
   )

Remove duplicates in the client code.

The solutions in NHibernate's world, in accordance to the SQL solutions:

Use the 'distinct' keyword.
The problems that exists in the SQL world still apply, and it can only be used in HQL, not it Criteria API.

Use subselects.
The syntax in HQL:

   from   Post p
   where exists
   (
      from Comment c
      where c.Post = p
      and c.Name = 'Ken Egozi'
   )

and in Criteria API:

 var commentsByKenEgozi = DetachedCriteria.For<comment>()
     .Add(Restrictions.Eq("Name", "Ken Egozi"))
     .Add(Restrictions.EqProperty("Post.Id", "p.Id"))
     .SetProjection(NHibernate.Criterion.Projections.Id());
 
  var posts = session.CreateCriteria(typeof (Post), "p")
     .Add(Subqueries.Exists(commentsByKenEgozi))
     .List<post>();</comment>

Remove duplicates in client code.
That's actually pretty easy with NHibernate, thanks to the result transformers. all you need to do is add .SetResultTransformer(new DistinctRootEntityResultTransformer()) to either your query, or criteria, and NHibernate will remove duplicate entries from the resulted list.
so, using the same hql as in the first example, you can write
```
 var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   var posts = session.CreateQuery(hql)
      .SetResultTransformer(new DistinctRootEntityResultTransformer())
      .List<post>();
```

Get unique results from joined queries

markweee — Wed, 30 Mar 2011 11:28:01 GMT

Revision 5 posted to How to by markweee on 30/03/2011 08:28:01 a.m.

Get unique results from joined queries

Filed under: query

Problem:

A recurring issue that new NHibernate users keep asking about, is the fact that they sometimes get duplicate results from their queries

For example, take a look at the next model:

where Comment.Name refer to the name of the person who wrote the comment.

If you'd want to issue a query on Post that joins to Comment, say "all of the posts that were commented by 'Ken Egozi'", the next hql query should do the trick:

   select  p
   from    Post p
   join    p.Comments c
   where   c.Name = 'Ken Egozi'";

So, you go ahead and

   var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   var posts = session.CreateQuery(hql)
      .List<post>();

Assuming the next data is in the DB:

  Post#1

    Comment by 'Ken Egozi'
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

  Post#2
    Comment by 'Fabio Maulo'

  Post#3
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

Explanation:

The said hql query (or an equivalent Criteria) is translated to the joined SELECT clause

   SELECT  {p.*}
   FROM    Posts p
     JOIN  Comments c ON c.PostId = p.Id
   WHERE   c.[Name] = 'Ken Egozi'

where {p.*} is substituted by the list of fields needed to satisfy a Post object. Running this SQL query directly on the data detailed above, will result with three lines in the resultset.

Solutions

There are three solutions to that in SQL world:

The DISTINCT keyword, when added on the fields of Posts, will ensure that there will be no duplicate lines. there are a few problems with that. Some RDBMS systems will not allow DISTINCT over certain data types, like the blob types in SQL Server. And if you also need to retrieve the joined data, then the DISTINCT keyword will be useless.

Using a subselect

   SELECT *
   FROM   Posts p
   WHERE EXISTS
   (
      SELECT 1
      FROM   Comments c
      WHERE  c.PostId = p.Id
        AND  c.[Name] = 'Ken Egozi'
   )

Remove duplicates in the client code.

The solutions in NHibernate's world, in accordance to the SQL solutions:

Use the 'distinct' keyword.
The problems that exists in the SQL world still apply, and it can only be used in HQL, not it Criteria API.

Use subselects.
The syntax in HQL:

   from   Post p
   where exists
   (
      from Comment c
      where c.Post = p
      and c.Name = 'Ken Egozi'
   )

and in Criteria API:

 var commentsByKenEgozi = DetachedCriteria.For<comment>()
     .Add(Restrictions.Eq("Name", "Ken Egozi"))
     .Add(Restrictions.EqProperty("Post.Id", "p.Id"))
     .SetProjection(NHibernate.Criterion.Projections.Id());
 
  var posts = session.CreateCriteria(typeof (Post), "p")
     .Add(Subqueries.Exists(commentsByKenEgozi))
     .List<post>();</comment>

Remove duplicates in client code.
That's actually pretty easy with NHibernate, thanks to the result transformers. all you need to do is add .SetResultTransformer(new DistinctRootEntityResultTransformer()) to either your query, or criteria, and NHibernate will remove duplicate entries from the resulted list.
so, using the same hql as in the first example, you can write
```
 var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   var posts = session.CreateQuery(hql)
      .SetResultTransformer(new DistinctRootEntityResultTransformer())
      .List<post>();
```

Get unique results from joined queries

Woil — Thu, 18 Sep 2008 16:10:22 GMT

Revision 4 posted to How to by Woil on 18/09/2008 01:10:22 p.m.

Get unique results from joined queries

Filed under: query

Problem:

A recurring issue that new NHibernate users keep asking about, is the fact that they sometimes get duplicate results from their queries

For example, take a look at the next model:

where Commment.Name Comment.Name refer to the name of the person who wrote the comment.

If you'd want to issue a query on Post that joins to Comment, say "all of the posts that were commented by 'Ken Egozi'", the next hql query should do the trick:

   select  p
   from    Post p
   join    p.Comments c
   where   c.Name = 'Ken Egozi'";

So, you go ahead and

   var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   var posts = session.CreateQuery(hql)
      .List<post>();

Assuming the next data is in the DB:

  Post#1

    Comment by 'Ken Egozi'
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

  Post#2
    Comment by 'Fabio Maulo'

  Post#3
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

Explanation:

The said hql query (or an equivalent Criteria) is translated to the joined SELECT clause

   SELECT  {p.*}
   FROM    Posts p
     JOIN  Comments c ON c.PostId = p.Id
   WHERE   c.[Name] = 'Ken Egozi'

where {p.*} is substituted by the list of fields needed to satisfy a Post object. Running this SQL query directly on the data detailed above, will result with three lines in the resultset.

Solutions

There are three solutions to that in SQL world:

The DISTINCT keyword, when added on the fields of Posts, will ensure that there will be no duplicate lines. there are a few problems with that. Some RDBMS systems will not allow DISTINCT over certain data types, like the blob types in SQL Server. And if you also need to retrieve the joined data, then the DISTINCT keyword will be useless.

Using a subselect

   SELECT *
   FROM   Posts p
   WHERE EXISTS
   (
      SELECT 1
      FROM   Comments c
      WHERE  c.PostId = p.Id
        AND  c.[Name] = 'Ken Egozi'
   )

Remove duplicates in the client code.

The solutions in NHibernate's world, in accordance to the SQL solutions:

Use the 'distinct' keyword.
The problems that exists in the SQL world still apply, and it can only be used in HQL, not it Criteria API.

Use subselects.
The syntax in HQL:

   from   Post p
   where exists
   (
      from Comment c
      where c.Post = p
      and c.Name = 'Ken Egozi'
   )

and in Criteria API:

 var commentsByKenEgozi = DetachedCriteria.For<comment>()
     .Add(Restrictions.Eq("Name", "Ken Egozi"))
     .Add(Restrictions.EqProperty("Post.Id", "p.Id"))
     .SetProjection(NHibernate.Criterion.Projections.Id());
 
  var posts = session.CreateCriteria(typeof (Post), "p")
     .Add(Subqueries.Exists(commentsByKenEgozi))
     .List<post>();</comment>

Remove duplicates in client code.
That's actually pretty easy with NHibernate, thanks to the result transformers. all you need to do is add .SetResultTransformer(new DistinctRootEntityResultTransformer()) to either your query, or criteria, and NHibernate will remove duplicate entries from the resulted list.
so, using the same hql as in the first example, you can write
```
 var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   var posts = session.CreateQuery(hql)
      .SetResultTransformer(new DistinctRootEntityResultTransformer())
      .List<post>();
```

Get unique results from joined queries

Ken Egozi — Fri, 12 Sep 2008 14:43:10 GMT

Revision 3 posted to How to by Ken Egozi on 12/09/2008 11:43:10 a.m.

Get unique results from joined queries

Problem:

A recurring issue that new NHibernate users keep asking about, is the fact that they sometimes get duplicate results from their queries

For example, take a look at the next model:

where Commment.Name refer to the name of the person who wrote the comment.

If you'd want to issue a query on Post that joins to Comment, say "all of the posts that were commented by 'Ken Egozi'", the next hql query should do the trick:

   select  p
   from    Post p
   join    p.Comments c
   where   c.Name = 'Ken Egozi'";

So, you go ahead and

   var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   var posts = session.CreateQuery(hql)
      .List<post>();

Assuming the next data is in the DB:

  Post#1

    Comment by 'Ken Egozi'
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

  Post#2
    Comment by 'Fabio Maulo'

  Post#3
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

Explanation:

The said hql query (or an equivalent Criteria) is translated to the joined SELECT clause

   SELECT  {p.*}
   FROM    Posts p
     JOIN  Comments c ON c.PostId = p.Id
   WHERE   c.[Name] = 'Ken Egozi'

where {p.*} is substituted by the list of fields needed to satisfy a Post object. Running this SQL query directly on the data detailed above, will result with three lines in the resultset.

Solutions

There are three solutions to that in SQL world:

The DISTINCT keyword, when added on the fields of Posts, will ensure that there will be no duplicate lines. there are a few problems with that. Some RDBMS systems will not allow DISTINCT over certain data types, like the blob types in SQL Server. And if you also need to retrieve the joined data, then the DISTINCT keyword will be useless.

Using a subselect

   SELECT *
   FROM   Posts p
   WHERE EXISTS
   (
      SELECT 1
      FROM   Comments c
      WHERE  c.PostId = p.Id
        AND  c.[Name] = 'Ken Egozi'
   )

Remove duplicates in the client code.

The solutions in NHibernate's world, in accordance to the SQL solutions:

Use the 'distinct' keyword.
The problems that exists in the SQL world still apply, and it can only be used in HQL, not it Criteria API.

Use subselects.
The syntax in HQL:

   from   Post p
   where exists
   (
      from Comment c
      where c.Post = p
      and c.Name = 'Ken Egozi'
   )

and in Criteria API:

 var commentsByKenEgozi = DetachedCriteria.For<comment>()
     .Add(Restrictions.Eq("Name", "Ken Egozi"))
     .Add(Restrictions.EqProperty("Post.Id", "p.Id"))
     .SetProjection(NHibernate.Criterion.Projections.Id());
 
  var posts = session.CreateCriteria(typeof (Post), "p")
     .Add(Subqueries.Exists(commentsByKenEgozi))
     .List<post>();</comment>

Remove duplicates in client code.
That's actually pretty easy with NHibernate, thanks to the result transformers. all you need to do is add .SetResultTransformer(new DistinctRootEntityResultTransformer()) to either your query, or criteria, and NHibernate will remove duplicate entries from the resulted list.
so, using the same hql as in the first example, you can write
```
 var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   var posts = session.CreateQuery(hql)
      .SetResultTransformer(new DistinctRootEntityResultTransformer())
      .List<post>();
```

Get unique results from joined queries

Fabio Maulo — Fri, 12 Sep 2008 14:34:49 GMT

Revision 2 posted to How to by Fabio Maulo on 12/09/2008 11:34:49 a.m.

Get unique results from joined queries

Problem:

A recurring issue that new NHibernate users keep asking about, is the fact that they sometimes get duplicate results from their queries

For example, take a look at the next model:

where Commment.Name refer to the name of the person who wrote the comment.

If you'd want to issue a query on Post that joins to Comment, say "all of the posts that were commented by 'Ken Egozi'", the next hql query should do the trick:

   select  p
   from    Post p
   join    p.Comments c
   where   c.Name = 'Ken Egozi'";

So, you go ahead and

   var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   ";
   var posts = session.CreateQuery(hql)
      .List<post>();

Assuming the next data is in the DB:
  Post#1
    Comment by 'Ken Egozi'
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

  Post#2
    Comment by 'Fabio Maulo'

  Post#3
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

you'd expect the list 'posts' to include two posts: Post#1 and Post#3.

However, if you'd look into posts, you'll see that it has three entries, two entries pointing to Post#1 and one entry pointing to Post#3

Explanation:

The said hql query (or an equivalent Criteria) is translated to the joined SELECT clause

   SELECT  {p.*}
   FROM    Posts p
     JOIN  Comments c ON c.PostId = p.Id
   WHERE   c.[Name] = 'Ken Egozi'

where {p.*} is substituted by the list of fields needed to satisfy a Post object. Running this SQL query directly on the data detailed above, will result with three lines in the resultset.

Solutions

There are three solutions to that in SQL world:

The DISTINCT keyword, when added on the fields of Posts, will ensure that there will be no duplicate lines. there are a few problems with that. Some RDBMS systems will not allow DISTINCT over certain data types, like the blob types in SQL Server. And if you also need to retrieve the joined data, then the DISTINCT keyword will be useless.

Using a subselect

   SELECT *
   FROM   Posts p
   WHERE EXISTS
   (
      SELECT 1
      FROM   Comments c
      WHERE  c.PostId = p.Id
        AND  c.[Name] = 'Ken Egozi'
   )

Remove duplicates in the client code.

The solutions in NHibernate's world, in accordance to the SQL solutions:

Use the 'distinct' keyword.
The problems that exists in the SQL world still apply, and it can only be used in HQL, not it Criteria API.

Use subselects.
The syntax in HQL:

   from   Post p
   where exists
   (
      from Comment c
      where c.Post = p
      and c.Name = 'Ken Egozi'
   )

and in Criteria API:

 var commentsByKenEgozi = DetachedCriteria.For<comment>()
     .Add(Restrictions.Eq("Name", "Name", "Ken Egozi"))
     "))
     .Add(Restrictions.EqProperty("Post.Id", "p.Id"))
     "Post.Id", "p.Id"))
     .SetProjection(NHibernate.Criterion.Projections.Id());
 
  var posts = session.CreateCriteria(typeof session.CreateCriteria(typeof (Post), "p")
     "p")
     .Add(Subqueries.Exists(commentsByKenEgozi))
     .List<post>();</comment>

Remove duplicates in client code.
That's actually pretty easy with NHibernate, thanks to the result transformers. all you need to do is add .SetResultTransformer(new DistinctRootEntityResultTransformer()) to either your query, or criteria, and NHibernate will remove duplicate entries from the resulted list.
so, using the same hql as in the first example, you can write
```
 var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   ";
   var posts = session.CreateQuery(hql)
      .SetResultTransformer(new SetResultTransformer(new DistinctRootEntityResultTransformer())
      .List<post>();
```

Get unique results from joined queries

Ken Egozi — Fri, 12 Sep 2008 07:32:51 GMT

Revision 1 posted to How to by Ken Egozi on 12/09/2008 04:32:51 a.m.

Problem:

A recurring issue that new NHibernate users keep asking about, is the fact that they sometimes get duplicate results from their queries

For example, take a look at the next model:

where Commment.Name refer to the name of the person who wrote the comment.

If you'd want to issue a query on Post that joins to Comment, say "all of the posts that were commented by 'Ken Egozi'", the next hql query should do the trick:

   select  p
   from    Post p
   join    p.Comments c
   where   c.Name = 'Ken Egozi'";

So, you go ahead and

   var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   var posts = session.CreateQuery(hql)
      .List<post>();

Assuming the next data is in the DB:
  Post#1
    Comment by 'Ken Egozi'
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

  Post#2
    Comment by 'Fabio Maulo'

  Post#3
    Comment by 'Fabio Maulo'
    Comment by 'Ken Egozi'

you'd expect the list 'posts' to include two posts: Post#1 and Post#3.

However, if you'd look into posts, you'll see that it has three entries, two entries pointing to Post#1 and one entry pointing to Post#3

Explanation:

The said hql query (or an equivalent Criteria) is translated to the joined SELECT clause

   SELECT  {p.*}
   FROM    Posts p
     JOIN  Comments c ON c.PostId = p.Id
   WHERE   c.[Name] = 'Ken Egozi'

where {p.*} is substituted by the list of fields needed to satisfy a Post object. Running this SQL query directly on the data detailed above, will result with three lines in the resultset.

Solutions

There are three solutions to that in SQL world:

The DISTINCT keyword, when added on the fields of Posts, will ensure that there will be no duplicate lines. there are a few problems with that. Some RDBMS systems will not allow DISTINCT over certain data types, like the blob types in SQL Server. And if you also need to retrieve the joined data, then the DISTINCT keyword will be useless.

Using a subselect

   SELECT *
   FROM   Posts p
   WHERE EXISTS
   (
      SELECT 1
      FROM   Comments c
      WHERE  c.PostId = p.Id
        AND  c.[Name] = 'Ken Egozi'
   )

Remove duplicates in the client code.

The solutions in NHibernate's world, in accordance to the SQL solutions:

Use the 'distinct' keyword.
The problems that exists in the SQL world still apply, and it can only be used in HQL, not it Criteria API.

Use subselects.
The syntax in HQL:

   from   Post p
   where exists
   (
      from Comment c
      where c.Post = p
      and c.Name = 'Ken Egozi'
   )

and in Criteria API:

  var commentsByKenEgozi = DetachedCriteria.For<comment>()
     .Add(Restrictions.Eq("Name", "Ken Egozi"))
     .Add(Restrictions.EqProperty("Post.Id", "p.Id"))
     .SetProjection(NHibernate.Criterion.Projections.Id());
 
  var posts = session.CreateCriteria(typeof (Post), "p")
     .Add(Subqueries.Exists(commentsByKenEgozi))
     .List<post>();</comment>

Remove duplicates in client code.
That's actually pretty easy with NHibernate, thanks to the result transformers. all you need to do is add .SetResultTransformer(new DistinctRootEntityResultTransformer()) to either your query, or criteria, and NHibernate will remove duplicate entries from the resulted list.
so, using the same hql as in the first example, you can write
```
   var hql = @"
      select  p
      from    Post p
      join    p.Comments c
      where   c.Name = 'Ken Egozi'";
   var posts = session.CreateQuery(hql)
      .SetResultTransformer(new DistinctRootEntityResultTransformer())
      .List<post>();
```

Pre-Generate Lazy Loading Proxies

John Davidson — Thu, 08 Sep 2011 00:18:34 GMT

Current revision posted to How to by John Davidson on 07/09/2011 09:18:34 p.m.

Pre-Generate Lazy Loading Proxies

Filed under: lazy loading

Download the latest binaries for NHibernate ProxyGenerators
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:
..\..\..\lib\bin\net-2.0\NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG.exe: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.
You're done! Pre-generated lazy loading proxies can be used with NHibernate to Run in Medium Trust

Sample Commands

Generate proxies for ActiveRecord
NHPG.exe /g:activerecord /o:Example.ActiceRecordDomain.Proxies.dll Example.ActiveRecordDomain.dll
Generate proxies with multiple class mapping assemblies Research Papers AND Term Papers
NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain1.dll Example.Domain2.dll

Generate proxies with a custom Dialect Essays AND Dissertations AND Theses
NHPG.exe /d:NHibernate.Dialect.Oracle9Dialect /o:Example.Domain.Proxies.dll Example.Domain.dll

Pre-Generate Lazy Loading Proxies

markweee — Wed, 30 Mar 2011 11:30:52 GMT

Revision 12 posted to How to by markweee on 30/03/2011 08:30:52 a.m.

Pre-Generate Lazy Loading Proxies

Filed under: lazy loading

Download the latest binaries for NHibernate ProxyGenerators
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:
..\..\..\lib\bin\net-2.0\NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG.exe: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.
You're done! Pre-generated lazy loading proxies can be used with NHibernate to Run in Medium Trust

Sample Commands

Generate proxies for ActiveRecord
NHPG.exe /g:activerecord /o:Example.ActiceRecordDomain.Proxies.dll Example.ActiveRecordDomain.dll
Generate proxies with multiple class mapping assemblies Research Papers AND Term Papers
NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain1.dll Example.Domain2.dll
Generate proxies with a custom Dialect Essays AND Dissertations AND Theses
NHPG.exe /d:NHibernate.Dialect.Oracle9Dialect /o:Example.Domain.Proxies.dll Example.Domain.dll

Pre-Generate Lazy Loading Proxies

Bill Pierce — Wed, 08 Oct 2008 18:03:24 GMT

Revision 11 posted to How to by Bill Pierce on 08/10/2008 03:03:24 p.m.

Pre-Generate Lazy Loading Proxies

Filed under: lazy loading

Download the latest binaries for NHibernate ProxyGenerators
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:
..\..\..\lib\bin\net-2.0\NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG.exe: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.
You're done! Pre-generated lazy loading proxies can be used with NHibernate to Run in Medium Trust

Sample Commands

Generate proxies for ActiveRecord
NHPG.exe /g:activerecord /o:Example.ActiceRecordDomain.Proxies.dll Example.ActiveRecordDomain.dll
Generate proxies with multiple class mapping assemblies
NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain1.dll Example.Domain2.dll
Generate proxies with a custom Dialect
NHPG.exe /d:NHibernate.Dialect.Oracle9Dialect /o:Example.Domain.Proxies.dll Example.Domain.dll

Pre-Generate Lazy Loading Proxies

Bill Pierce — Tue, 23 Sep 2008 18:22:57 GMT

Revision 10 posted to How to by Bill Pierce on 23/09/2008 03:22:57 p.m.

Pre-Generate Lazy Loading Proxies

Download the latest binaries for NHibernate ProxyGenerators
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:
..\..\..\lib\bin\net-2.0\NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG.exe: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.
You're done! Pre-generated lazy loading proxies can be used with NHibernate to Run in Medium Trust

Sample Commands

Generate proxies for ActiveRecord
NHPG.exe /g:activerecord /o:Example.ActiceRecordDomain.Proxies.dll Example.ActiveRecordDomain.dll
Generate proxies with multiple class mapping assemblies
NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain1.dll Example.Domain2.dll

Pre-Generate Lazy Loading Proxies

Bill Pierce — Tue, 23 Sep 2008 18:11:02 GMT

Revision 9 posted to How to by Bill Pierce on 23/09/2008 03:11:02 p.m.

Pre-Generate Lazy Loading Proxies

Download the latest binaries for NHibernate ProxyGenerators
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:
..\..\..\lib\bin\net-2.0\NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG.exe: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.
You're done! Pre-generated lazy loading proxies can be used with NHibernate to Run in Medium Trust

Sample Commands

Pre-Generate Lazy Loading Proxies
- Generate proxies for ActiveRecord
  NHPG.exe /g:activerecord /o:Example.ActiceRecordDomain.Proxies.dll Example.ActiveRecordDomain.dll
- Generate proxies with multiple class mapping assemblies
  NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain1.dll Example.Domain2.dll

Pre-Generate Lazy Loading Proxies

Bill Pierce — Tue, 23 Sep 2008 18:09:19 GMT

Revision 8 posted to How to by Bill Pierce on 23/09/2008 03:09:19 p.m.

Pre-Generate Lazy Loading Proxies

Download the latest binaries for NHibernate ProxyGenerators
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:
..\..\..\lib\bin\net-2.0\NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG.exe: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.
You're done! Pre-generated lazy loading proxies can be used with NHibernate to Run in Medium Trust

Sample Commands

Pre-Generate Lazy Loading Proxies for ActiveRecord
NHPG.exe /g:activerecord /o:Example.ActiceRecordDomain.Proxies.dll Example.ActiveRecordDomain.dll

Pre-Generate Lazy Loading Proxies

Bill Pierce — Tue, 23 Sep 2008 03:58:50 GMT

Revision 7 posted to How to by Bill Pierce on 23/09/2008 12:58:50 a.m.

Pre-Generate Lazy Loading Proxies

***This is preliminary documentation***

Download the latest binaries for NHibernate ProxyGenerators
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:
..\..\..\lib\NHPG .\..\..\lib\bin\net-2.0\NHPG.exe /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG

NHPG.exe: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.
You're done! Pre-generated lazy loading proxies can be used with NHibernate to Run in Medium Trust

Pre-Generate Lazy Loading Proxies

Bill Pierce — Mon, 22 Sep 2008 17:19:24 GMT

Revision 6 posted to How to by Bill Pierce on 22/09/2008 02:19:24 p.m.

Pre-Generate Lazy Loading Proxies

***This is preliminary documentation***

Download the latest binaries for NHibernate ProxyGenerators
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:
..\..\..\lib\NHPG /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.
You're done! Pre-generated lazy loading proxies can be used with NHibernate to Run in Medium Trust

Pre-Generate Lazy Loading Proxies

Bill Pierce — Mon, 22 Sep 2008 17:15:02 GMT

Revision 5 posted to How to by Bill Pierce on 22/09/2008 02:15:02 p.m.

Pre-Generate Lazy Loading Proxies

***This is preliminary documentation***

Download the latest binaries for [howtonh:/media/g/proxygenerators/default.aspx|NHibernate NHibernate ProxyGenerators]
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:
..\..\..\lib\NHPG /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.

Pre-Generate Lazy Loading Proxies

Bill Pierce — Mon, 22 Sep 2008 17:14:41 GMT

Revision 4 posted to How to by Bill Pierce on 22/09/2008 02:14:41 p.m.

Pre-Generate Lazy Loading Proxies

***This is preliminary documentation***

Download the latest binaries for [howtonh:/media/g/proxygenerators/default.aspx|NHibernate ProxyGenerators]ProxyGenerators]
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:
..\..\..\lib\NHPG /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.

Pre-Generate Lazy Loading Proxies

Bill Pierce — Mon, 22 Sep 2008 17:14:24 GMT

Revision 3 posted to How to by Bill Pierce on 22/09/2008 02:14:24 p.m.

Pre-Generate Lazy Loading Proxies

***This is preliminary documentation***

Download the latest binaries for NHibernate Proxy[[howtonh:/media/g/proxygenerators/default.aspx|NHibernate ProxyGenerators]]Generators[howtonh:/media/g/proxygenerators/default.aspx|NHibernate ProxyGenerators]]

Extract the binaries to your "lib" directory relative to your source files

Open a command prompt and navigate the to "bin" directory in your web project.

Enter the following command:
..\..\..\lib\NHPG /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)

Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.

Pre-Generate Lazy Loading Proxies

Bill Pierce — Mon, 22 Sep 2008 17:13:56 GMT

Revision 2 posted to How to by Bill Pierce on 22/09/2008 02:13:56 p.m.

Pre-Generate Lazy Loading Proxies

***This is preliminary documentation***

Download the latest binaries for NHibernate ProxyGeneratorsProxy[[howtonh:/media/g/proxygenerators/default.aspx|NHibernate ProxyGenerators]]Generators
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:
..\..\..\lib\NHPG /o:Example.Domain.Proxies.dll Example.Domain.dll

NHPG: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.

Pre-Generate Lazy Loading Proxies

Bill Pierce — Mon, 22 Sep 2008 17:12:27 GMT

Revision 1 posted to How to by Bill Pierce on 22/09/2008 02:12:27 p.m.

***This is preliminary documentation***

Download the latest binaries for NHibernate ProxyGenerators
Extract the binaries to your "lib" directory relative to your source files
Open a command prompt and navigate the to "bin" directory in your web project.
Enter the following command:

NHPG: The console application that generates the proxies. Included in the binary distribution from step 1
/o: The path to the assembly that will be generated by NHPG
Example.Domain.dll: The assembly that contains your NHibernate Mappings (hbm.xml files)
Add 'proxyfactory.factory_class' to your NHibernate configuration file:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
    <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property>
    <property name="connection.connection_string">Server=(local);Database=Development;Trusted_Connection=True;</property>
    <mapping assembly="Example.Domain" />

    <property name="proxyfactory.factory_class">CastleStaticProxyFactoryFactory, Example.Domain.Proxies</property>
</session-factory>
</hibernate-configuration>
Replace Example.Domain.Proxies with the name of the assembly used for argument '/o' in Step 4.

Lazy Loaded One-To-One With NHibernate

John Davidson — Thu, 08 Sep 2011 00:13:38 GMT

Current revision posted to How to by John Davidson on 07/09/2011 09:13:38 p.m.

Lazy Loaded One-To-One With NHibernate

UPDATE 20081114

The one-to-one solution I had posted turned out not to work for updates, :(, in the end I had to use a many-to-one map with a unique foreign key association to get this to work, the updated example is below. Sorry for my EPIC FAIL :)...

G'day,

I am working on something at the moment and I am storing BLOB data for documents in the database, I am storing things like name and data which is a binary field. |
Now I wan't to load the binary data as loading this all the time is very inneficient. So to get this to work I had to split this to two tables, one with my meta data and another one-to-one
table to store the BLOB. NOW the fun began I created the two tables:

Documents
-------------------
(PK) Id
(FK Unique) DocumentFileId
Name

DocumentFiles
-------------------
(PK) Id
Data

From this I created my POCO classes for the Document and DocumentFile map.

public class Document {
    public int Id { get; set; }
    public string Name { get; set; }
    public DocumentFile DocumentFile { get; set; }
}

public class DocumentFile {
    public virtual int Id { get; set; }
    public virtual Document Document { get; set; }
    public virtual byte[] Data { get; set; }
}

Now on to the mappings, I thought this would be as easy as created a one-to-one mapping with lazy="proxy" set on the one-to-one on the Document class but this was not the case.
You NEED to set constrained="true" on the mapping, basically going from this post I found: http://www.hibernate.org/162.html#A5. Say we have A->B where this is a 1-1 relationship,
now without a constraint from A-B this means A can exist without B, so there is a possiblity that B is null, a Proxy to B will be not null and won't work here.

But when we know A and B will always belong together it is ok to create a Proxy for B. Now my final mapping files looks like so:

BUUUT as I soon found out if in the A mapping you constrain B it will mean it will try to insert B first and fail to generate a primary key with the foreign key generator, hence not working as expected, I had to change the mappings to use a many-to-one unique foreign key mapping to get this to work. I updated the mappings below, the main differences are highlighted below:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
<class name="NHibernateDocumentTest.Document, NHibernateDocumentTest" table="Documents" lazy="false">
    <id name="Id" column="Id" type="integer">
      <generator class="native" />
    </id>
    <property name="Name" column="Name" type="string" />
    <many-to-one name="DocumentFile" cascade="all-delete-orphan"
                 lazy="proxy" column="DocumentFileId" unique="true" />
</class>
</hibernate-mapping>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
<class name="NHibernateDocumentTest.DocumentFile, NHibernateDocumentTest" table="DocumentFiles" lazy="true">
    <id name="Id" column="Id" type="integer">
      <generator class="native" />
    </id>
    <property name="Data" column="Data" type="Byte[]" />
    <one-to-one name="Document" constrained="true" property-ref="DocumentFile" />
</class>
</hibernate-mapping>Graduate Diploma AND Phd Degree

And then we are done, this works fine. So the trick is for a one-to-one to work with Lazy loading you must use a unique foreign key associated with a many-to-one mapping to your child.Graduate Certificate AND Undergraduate Diploma AND Online Schools

Thanks
Stefan

Lazy Loaded One-To-One With NHibernate

markweee — Wed, 30 Mar 2011 11:06:31 GMT

Revision 3 posted to How to by markweee on 30/03/2011 08:06:31 a.m.

Lazy Loaded One-To-One With NHibernate

G'day,

Documents
-------------------
(PK) Id
(FK Unique) DocumentFileId
Name

DocumentFiles
-------------------
(PK) Id
Data

From this I created my POCO classes for the Document and DocumentFile map.

public class Document {
    public int Id { get; set; }
    public string Name { get; set; }
    public DocumentFile DocumentFile { get; set; }
}

public class DocumentFile {
    public virtual int Id { get; set; }
    public virtual Document Document { get; set; }
    public virtual byte[] Data { get; set; }
}

And then we are done, this works fine. So the trick is for a one-to-one to work with Lazy loading you must use a unique foreign key associated with a many-to-one mapping to your child. Graduate Certificate AND Undergraduate Diploma AND Online Schools

Thanks
Stefan

Lazy Loaded One-To-One With NHibernate

stefan.sedich — Fri, 14 Nov 2008 01:57:49 GMT

Revision 2 posted to How to by stefan.sedich on 13/11/2008 10:57:49 p.m.

Lazy Loaded One-To-One With NHibernate

G'day,

Documents
-------------------
(PK) Id
(FK Unique) DocumentFileId
Name

DocumentFiles
-------------------
(FK) PK) Id
Data

From this I created my POCO classes for the Document and DocumentFile map.

public class Document {
    public int Id { get; set; }
    public string Name { get; set; }
    public DocumentFile DocumentFile { get; set; }
}

public class DocumentFile {
    public virtual int Id { get; set; }
    public virtual Document Document { get; set; }
    public virtual byte[] Data { get; set; }
}

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
<class name="NHibernateDocumentTest.Document, NHibernateDocumentTest" table="Documents" lazy="false">
    <id name="Id" column="Id" type="integer">
      <generator class="native" />
    </id>
    <property name="Name" column="Name" type="string" />
    <one-to-one
    <many-to-one name="DocumentFile" cascade="all-delete-orphan"
                 lazy="proxy" constrained=column="DocumentFileId" unique="true" />
</class>
</hibernate-mapping>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
<class name="NHibernateDocumentTest.DocumentFile, NHibernateDocumentTest" table="DocumentFiles" lazy="true">
    <id name="Id" column="Id" type="integer">
      <generator class="foreign">
        <param name="property">Document</param>
      </generator>
    </id>    "native" />
    </id>
    <property name="Data" column="Data" type="Byte[]" />
    <one-to-one name="Document" fetch="select" constrained="true" property-ref="DocumentFile" />
</class>
</hibernate-mapping>

Basically the one-to-one in the Document has contraint for DocumentFile so these always belong together as is the case here, also I have set lazy to Proxy for this one-to-one.

And then we are done, this works fine. So the trick is for a one-to-one to work with Lazy loading you must have use a constraint on your relationship.
This can also be done unique foreign key associated with a Many-To-One where it is the case where A can exist without Bmany-to-one mapping to your child.

Thanks
Stefan

Lazy Loaded One-To-One With NHibernate

stefan.sedich — Thu, 13 Nov 2008 14:15:11 GMT

Revision 1 posted to How to by stefan.sedich on 13/11/2008 11:15:11 a.m.

Documents
-------------------
(PK) Id
Name

DocumentFiles
-------------------
(FK) Id
Data

From this I created my POCO classes for the Document and DocumentFile map.

public class Document {
    public int Id { get; set; }
    public string Name { get; set; }
    public DocumentFile DocumentFile { get; set; }
}

public class DocumentFile {
    public virtual int Id { get; set; }
    public virtual Document Document { get; set; }
    public virtual byte[] Data { get; set; }
}

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
<class name="NHibernateDocumentTest.Document, NHibernateDocumentTest" table="Documents" lazy="false">
    <id name="Id" column="Id" type="integer">
      <generator class="native" />
    </id>
    <property name="Name" column="Name" type="string" />
    <one-to-one name="DocumentFile" cascade="all-delete-orphan" lazy="proxy" constrained="true" />
</class>
</hibernate-mapping>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
<class name="NHibernateDocumentTest.DocumentFile, NHibernateDocumentTest" table="DocumentFiles" lazy="true">
    <id name="Id" column="Id" type="integer">
      <generator class="foreign">
        <param name="property">Document</param>
      </generator>
    </id>
    <property name="Data" column="Data" type="Byte[]" />
    <one-to-one name="Document" fetch="select" constrained="true" />
</class>
</hibernate-mapping>

Basically the one-to-one in the Document has contraint for DocumentFile so these always belong together as is the case here, also I have set lazy to Proxy for this one-to-one.

And then we are done, this works fine. So the trick is for a one-to-one to work with Lazy loading you must have a constraint on your relationship.
This can also be done with a Many-To-One where it is the case where A can exist without B.

Thanks
Stefan

Dynamically change user info in connection string

John Davidson — Thu, 08 Sep 2011 00:09:08 GMT

Current revision posted to How to by John Davidson on 07/09/2011 09:09:08 p.m.

Dynamically change user info in connection string

Filed under: Mapping, QuickStart

In some cases our clients has to use the same database user id in each connection, so they can use audit and security features of their database system (and their DBAs will be happy [:)]).Hill University AND Woodfield University

To do that in Nh We can use the ConnectionProvider facility. Just derive a class from the Corllins University standard DriverConnectionProvider class:Ashwood University Accreditation AND Rochville University Accreditation

public class DynamicConnectionProvider : DriverConnectionProvider
{
    private string _connectionString;
    public override void Configure(IDictionary<string, string> settings)
    {

        // Connection string in the configuration overrides named connection string
        if (!settings.TryGetValue(NHibernate.Cfg.Environment.ConnectionString,out _connectionString))
    _connectionString = GetNamedConnectionString(settings);

        if (_connectionString == null)
        {
            throw new HibernateException("Could not find connection string setting (set " 
                + NHibernate.Cfg.Environment.ConnectionString + " or " 
                + NHibernate.Cfg.Environment.ConnectionStringName + " property)");
        }
        ConfigureDriver(settings);
    }

This is necessary because the original connection string is private, but just copy the code from base method.

The real magic is in "ConnectionString" property, it is called when nh has to connect in a Session. You have to override it so you can make the changes you need.

protected override string ConnectionString
{
    get { return FixConnectionString(_connectionString); }
}

In this case FixConnectionString read the user info from some environment variable and inject it in the connection string.

Finally configure NH to use the ConnectionProvider:

            <property name="connection.provider">
                MyAssembly.DynamicConnectionProvider, MyAssembly
            </property>

Some useful articles here and here

Dynamically change user info in connection string

markweee — Wed, 30 Mar 2011 11:34:18 GMT

Revision 5 posted to How to by markweee on 30/03/2011 08:34:18 a.m.

Dynamically change user info in connection string

Filed under: Mapping, QuickStart

To do that in Nh We can use the ConnectionProvider facility. Just derive a class from the Corllins Universitystandard DriverConnectionProvider class: Ashwood University Accreditation AND Rochville University Accreditation

public class DynamicConnectionProvider : DriverConnectionProvider
{
    private string _connectionString;
    public override void Configure(IDictionary<string, string> settings)
    {

        // Connection string in the configuration overrides named connection string
        if (!settings.TryGetValue(NHibernate.Cfg.Environment.ConnectionString,out _connectionString))
    _connectionString = GetNamedConnectionString(settings);

        if (_connectionString == null)
        {
            throw new HibernateException("Could not find connection string setting (set " 
                + NHibernate.Cfg.Environment.ConnectionString + " or " 
                + NHibernate.Cfg.Environment.ConnectionStringName + " property)");
        }
        ConfigureDriver(settings);
    }

This is necessary because the original connection string is private, but just copy the code from base method.

The real magic is in "ConnectionString" property, it is called when nh has to connect in a Session. You have to override it so you can make the changes you need.

protected override string ConnectionString
{
    get { return FixConnectionString(_connectionString); }
}

In this case FixConnectionString read the user info from some environment variable and inject it in the connection string.

Finally configure NH to use the ConnectionProvider:

            <property name="connection.provider">
                MyAssembly.DynamicConnectionProvider, MyAssembly
            </property>

Some useful articles here and here

Dynamically change user info in connection string

Fabio Maulo — Sat, 29 Nov 2008 05:16:58 GMT

Revision 4 posted to How to by Fabio Maulo on 29/11/2008 02:16:58 a.m.

Dynamically change user info in connection string

Filed under: Mapping, QuickStart

In some cases our clients has to use the same database user id in each connection, so they can use audit and security features of their database system (and their DBAs will be happy [:)]).

To do that in Nh We can use the ConnectionProvider facility. Just derive a class from the standard DriverConnectionProvider class:

public class DynamicConnectionProvider : DriverConnectionProvider
{
    private string _connectionString;
    public override void Configure(IDictionary<string, string> settings)
    {

        // Connection string in the configuration overrides named connection string
        if (!settings.TryGetValue(NHibernate.Cfg.Environment.ConnectionString,out _connectionString))
    _connectionString = GetNamedConnectionString(settings);

        if (_connectionString == null)
        {
            throw new HibernateException("Could not find connection string setting (set " 
                + NHibernate.Cfg.Environment.ConnectionString + " or " 
                + NHibernate.Cfg.Environment.ConnectionStringName + " property)");
        }
        ConfigureDriver(settings);
    }

This is necessary because the original connection string is private, but just copy the code from base method.

The real magic is in "ConnectionString" property, it is called when nh has to connect in a Session. You have to override it so you can make the changes you need.

protected override string ConnectionString
{
    get { return FixConnectionString(_connectionString); }
}

In this case FixConnectionString read the user info from some environment variable and inject it in the connection string.

Finally configure NH to use the ConnectionProvider:

            <property name="connection.provider">
                MyAssembly.DynamicConnectionProvider, MyAssembly
            </property>

Some useful articles here and [[howtonh:howtonh:/blogs/nhibernate/archive/2008/09/18/extending-nhibernate-s-driverconnectionprovider.aspx|here]] here

Dynamically change user info in connection string

Fabio Maulo — Sat, 29 Nov 2008 05:14:55 GMT

Revision 3 posted to How to by Fabio Maulo on 29/11/2008 02:14:55 a.m.

Dynamically change user info in connection string

In some cases our clients has to use the same database user id in each connection, so they can use audit and security features of their database system (and their DBAs will be happy [:)]).

To do that in Nh We can use the ConnectionProvider facility. Just derive a class from the standard DriverConnectionProvider class:

public class DynamicConnectionProvider : DriverConnectionProvider
{
    private string _connectionString;
    
 
Override the Configure method:public override void Configure(IDictionary<string, Configure(IDictionary<string, string> settings)
    {

        // Connection string in the configuration overrides named connection string
        if (!settings.TryGetValue(NHibernate.Cfg.Environment.ConnectionString, !settings.TryGetValue(NHibernate.Cfg.Environment.ConnectionString,out _connectionString))
    _connectionString = GetNamedConnectionString(settings);

        if (_connectionString == null)
        {
            throw new HibernateException("Could not find connection string setting (set " 
                +                                  NHibernate.Cfg.Environment.ConnectionString NHibernate.Cfg.Environment.ConnectionString + " or " 
                +                                  NHibernate.Cfg.Environment.ConnectionStringName NHibernate.Cfg.Environment.ConnectionStringName + " property)");");
        }
        ConfigureDriver(settings);
    }

This is necessary because the original connection string is private, but just copy the code from base method.

The real magic is in "ConnectionString" property, it is called when nh has to connect in a Session. You have to override it so you can make the changes you need.

protected override string ConnectionString
{
    get { return FixConnectionString(_connectionString); }
}

In this case "FixConnectionString" FixConnectionString read the user info from some environment variable and inject it in the connection string.

Finally configure Nh NH to use the ConnectionProvider:

<property name="connection.provider">MyAssembly.DynamicConnectionProvider,

            <property name="connection.provider">
                MyAssembly.DynamicConnectionProvider, MyAssembly
            </property></property>

Some useful articles:

http://japikse.blogspot.com/2008/06/custom-connection-provider-with.html here and

http://nhforge.org/blogs/nhibernate/archive/2008/09/18/extending-nhibernate-s-driverconnectionprovider.aspx [[howtonh:howtonh:/blogs/nhibernate/archive/2008/09/18/extending-nhibernate-s-driverconnectionprovider.aspx|here]]

Dynamically change user info in connection string

oorduz — Sat, 29 Nov 2008 00:41:57 GMT

Revision 2 posted to How to by oorduz on 28/11/2008 09:41:57 p.m.

Dynamically change user info in connection string

In some cases our clients has to use the same database user id in each connection, so they can use audit and security features of their database system (and their DBAs will be happy [:)]).

To do that in Nh We can use the ConnectionProvider facility. Just derive a class from the standard DriverConnectionProvider class:

public class DynamicConnectionProvider : DriverConnectionProvider

{

private string _connectionString;

Override the Configure method:

public override void Configure(IDictionary<string, string> settings)

{

// Connection string in the configuration overrides named connection string

if (!settings.TryGetValue(NHibernate.Cfg.Environment.ConnectionString,

out _connectionString))

_connectionString = GetNamedConnectionString(settings);

if (_connectionString == null)

{

throw new HibernateException("Could not find connection string setting (set " + NHibernate.Cfg.Environment.ConnectionString + " or " + NHibernate.Cfg.Environment.ConnectionStringName + " property)");

}

ConfigureDriver(settings);

}

This is necessary because the original connection string is private, but just copy the code from base method.

The real magic is in "ConnectionString" property, it is called when nh has to connect in a Session. You have to override it so you can make the changes you need.

protected override string ConnectionString

{

get

{

return FixConnectionString(_connectionString);

}

In this case "FixConnectionString" read the user info from some environment variable and inject it in the connection string.

Finally configure Nh to use the ConnectionProvider:

<property name="connection.provider">MyAssembly.PsDynamicConnectionProvider, "connection.provider">MyAssembly.DynamicConnectionProvider, MyAssembly </property>

Some useful articles:

http://japikse.blogspot.com/2008/06/custom-connection-provider-with.html

and

http://nhforge.org/blogs/nhibernate/archive/2008/09/18/extending-nhibernate-s-driverconnectionprovider.aspx

Dynamically change user info in connection string

oorduz — Sat, 29 Nov 2008 00:29:02 GMT

Revision 1 posted to How to by oorduz on 28/11/2008 09:29:02 p.m.

In some cases our clients has to use the same database user id in each connection, so they can use audit and security features of their database system (and their DBAs will be happy [:)]).

To do that in Nh We can use the ConnectionProvider facility. Just derive a class from the standard DriverConnectionProvider class:

public class DynamicConnectionProvider : DriverConnectionProvider

{

private string _connectionString;

Override the Configure method:

public override void Configure(IDictionary<string, string> settings)

{

// Connection string in the configuration overrides named connection string

if (!settings.TryGetValue(NHibernate.Cfg.Environment.ConnectionString,

out _connectionString))

_connectionString = GetNamedConnectionString(settings);

if (_connectionString == null)

{

throw new HibernateException("Could not find connection string setting (set " + NHibernate.Cfg.Environment.ConnectionString + " or " + NHibernate.Cfg.Environment.ConnectionStringName + " property)");

}

ConfigureDriver(settings);

}

This necessary because the original connection string is private, but just copy the code from base method.

The real magic is in "ConnectionString" property, it is called when nh has to connect in a Session. You have to override it so you can make the changes you need.

protected override string ConnectionString

{

get

{

return FixConnectionString(_connectionString);

}

In this case "FixConnectionString" read the user info from some environment variable and inject it in the connection string.

Finally configure Nh to use the ConnectionProvider:

<property name="connection.provider">MyAssembly.PsDynamicConnectionProvider, MyAssembly </property>

Some useful articles:

http://japikse.blogspot.com/2008/06/custom-connection-provider-with.html

and

http://nhforge.org/blogs/nhibernate/archive/2008/09/18/extending-nhibernate-s-driverconnectionprovider.aspx

Mapping the same class to a view and a table using entity-name

John Davidson — Thu, 08 Sep 2011 00:04:52 GMT

Current revision posted to How to by John Davidson on 07/09/2011 09:04:52 p.m.

Mapping the same class to a view and a table using entity-name

Filed under: Session, Architecture, query, entity name

The Scenario

You have a single class which you must map to both a table and a database view (or perhaps another table). The view is returning records from the table itself, usually filtered, and the view may have more or less columns than the table. A more practical example is a multi tenant database, where a table has a tenant column, and the view filters the records to show only the ones associated with the current tenant. In this case, the backing table has a tenant column, but the view doesn't. To make things even more interesting, the table is in a separate database schema. For more details on this multi tenant architectural pattern see this article. Other possible uses for this mapping technique include dynamically mapping the same base class to multiple subclass tables, which is described here,

You want to map this in NHibernate, in a way that will allow you to specify which 'representation' of the entity you want to see, either the table containing records for all tenants, or the view containing records for the currently active tenant. Perhaps your system needs to access all the records for all tenants to perform auditing or cleanup. In all other cases, you only want to show the records filtered for the current tenant, via the mapped view.

So, can this be done? Thankfully, yes, but only if you like living on the cutting edge!

Prerequisites

In order to set this up with NHibernate, you will need to use the up and coming version 2.1, as we will be taking advantage of the new 'entity-name' feature. This means you will need to checkout and build the latest version of NHibernate. There's plenty of guidance online about this.

In this article, I'll be working against version 2.1.0.1001, revision 4099.

If you are using NHibernate.Linq, there's some special considerations that I'll explain later. You'll need to modify this library to take advantage of entity names, so you will need to checkout and build it from the nhcontrib project:

I'll be working against version 1.0.0.0, revision 803.

Setting up the mappings

The class we're using is fairly simple, as the magic happens in the mapping. Note that the TenantId property is nullable, as it wont be mapped when we are using the view, more on that later.


public class MyEntity {
	public virtual int Id { get; private set; }
	
	public virtual string MyProperty { get; set; }
	
	public virtual int? TenantId { get; private set; }
}

The database is also pretty straightforward, we have a table which maps to the entity class, and a view which returns records from that table. Notice that the view has no tenant id. Also notice that both of these objects are in different schemas. This just highlights the fact that the mappings for the two objects would have to be different, even if the properties were identical.


CREATE TABLE [AllItemsSchema].[MyEntity](

	[ID] int not null,

	[MyProperty] varchar(200) NULL,
	
	[TenantId] int not null,
	
	CONSTRAINT [PK_MyEntity] PRIMARY KEY CLUSTERED ([ID])
)



CREATE VIEW [TenantSpecificSchema].[MyEntity]

AS

SELECT [ID], [MyProperty] FROM [AllItemsSchema].[MyEntity] WHERE [TenantId] = dbo.GetCurrentTenant()

So far so good. Now we move on to the mappings. Firstly, the table specific mapping. This will allow us to access all of the records for a particular entity, regardless of the tenant they are associated with.


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="Table" schema="`AllItemsSchema`">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
		<property name="TenantId" not-null="true" />
	</class>
</hibernate-mapping>

Some things to notice here are:

The 'schema' attribute is set to 'AllItemsSchema'
The new 'entity-name' attribute is specified. In this case we are keeping it fairly simple, in the real world you would want to use something that's unique for each entity.
The TenantId property is mapped

The rest of the mapping is the exactly the same as you would expect. As I noted above, the entity name here is deliberately simplistic. Its also worth mentioning that the entity name is used to uniquely identity an entity mapping across the entire session factory, so you cant repeat it on different class mappings. Next, on to the mapping of the view, which will provide only the records for the currently active tenant.


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="View" schema="`TenantSpecificSchema`" schema-action="none">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
	</class>
</hibernate-mapping>

This is where things get interesting:

We have used the same table and class name, but notice that the 'entity-name' is different
We have a different database schema 'TenantSpecificSchema'
The TenantId property is absent as the view does not provide this
The new 'schema-action' is set to none, this will prevent NHibernate from including this mapping in its schema export, it would otherwise attempt to create a table for this view

Although we are using the same class in both cases, the mappings can be quite different. In this example I've included the TenantId property on the entity class even though it will always be null when the view mapping is used. Whether you want to do this yourself is a matter of taste. One possibility would be to implement the TenantId property with an explicit interface, which would hide it from the consumers of the class unless needed.

Now that we have the mappings we can spin up a session factory using your favorite technique. Because we have used entity names for both of our mappings, you will see that we cant just store and retrieve entities by their type as usual. The entities are no longer identified by their types, but their entity name instead. Initially, I had planned to specify the entity name only for one of the mappings, and leave the other mapping as a 'default' with just its [Type] 'name' specified, but as I will explain later in more detail, this wont work as expected. If you want to reliably use entity name on one mapping of the class, you must use an entity name on them all.

Entity name and the ISession

In the latest revision of NHibernate, all the methods of ISession which take a System.Type have been overloaded to accept a string specifying the entity name. Apart form this, working with entity name mappings is exactly the same as their Type counterparts. If you are using a generic implementation of IRepository, things get even easier, as you can control the entity name in a single place, for example:


public enum EntityNameMode {
	Default,
	Table,
	View
}

public class NHibernateRepository<TEntity, TKey> : IRepository<TEntity, TKey> {
	public NHibernateRepository(ISession session, EntityNameMode mode) {
		this.session = session;
		this.mode = mode;
	}
	
	public TEntity Get(TKey key) {
		return (TEntity)session.Get(GetEntityName(), key);
	}
	
	public IList<TEntity> List() {
		return session.CreateCriteria(GetEntityName()).List<TEntity>();
	}
	
	public void SaveOrUpdate(TEntity entity) {
		session.SaveOrUpdate(GetEntityName(), entity);
	}
	
	private string GetEntityName() {
		switch (mode) {
			case EntityNameMode.Table: return "Table";
			case EntityNameMode.View: return "View";
			default: return typeof(TEntity).FullName;
		}
	}
	
	private ISession session;
	private EntityNameMode mode;
}

The entity name to use is based on the parameter we pass into the repository. In the real world you will want to use something more sophisticated to control the entity names. By specifying the Table mode when creating this repository, all the operations we perform against it will now deal with the records for all tenants. If we only want to deal with the records for a specific tenant, then we pass in the View mode.

	
	//this repository will work with data for all tenants
	var allTenantsRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.Table);

	//this repository will work with data for the current tenant only
	var currentTenantRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.View);

One thing that's important to realize is that internally, NHibernate implicitly creates an entity name whether you specify one explicitly or not. The entity name it uses by default is the FullName of the mapped type. This means that passing in the Type.FullName to the methods accepting a string has the same effect as passing in the System.Type itself. This can make it easier to manage your Repository implementation as you can use the string overloads exclusively, and pass in the type name when no specific entity name is required.

Now we have a repository that we can use to work with the two different profiles for our entities, as well as falling back to the standard behavior when no entity name mappings are required. This approach can be extended in any number of ways to support various complex mapping scenarios.

Its worth mentioning that you can also specify the entity name via IInterceptor.GetEntityName(object), but I haven't done that here because it only kicks in when saving or updating transient instances, as far as I could tell. You still have to supply the entity name to the ISession methods when querying the database, and I prefer to keep the entity name behavior in one place.

If you want to use NHibernate.Linq with this approach then you will soon find that there's currently (r.803) no way to specify the entity name when using the Linq<T> extension method on ISession. Not to fear, there's a fairly straightforward way to provide this feature with minimal impact on any querying code you may have.

Using Entity Name with Linq to NHibernate

Lets start by adding a protected property to our Repository implementation which will provide us with an INHibernateQueryable<T>. All we need to know about that type for now is that its returned from the ISession.Linq<T> extension method.

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			return session.Linq<TEntity>();
		}
	}

	//the rest of the repository is exactly the same...

We can now use Linq functionality in our repository by starting with that property. Lets add a useful Find() method to our repository that accepts a predicate which we can pass to the Linq implementation.

	
	public TEntity Find(Expression<Func<TEntity, bool>> predicate) {
		return Linq.Where(predicate).FirstOrDefault();
	}

There's one problem with this approach however. As you can see in the Linq property, we are passing in the current generic type of our repository. This means that our entity name mappings are not being used, and even worse than that, NHibernate will throw an error informing us that the type in question could not be found. This is to be expected, recall that we are overriding the implicit entity name, which defaults to the mapped types name, with our own.

The current implementation of NHibernate.Linq is based on ICriteria, and ISession.CreateCriteria has an overload that will accept an entity name, just like all the other ISession methods. Because the entity name (or the Type) of an ICriteria can not be modified after it is created, we must control the creation of the ICriteria ourselves. The way I chose to do it was by adding a function callback to the QueryOptions object in NHibernate.Linq. This callback accepts the Linq ISession and the current expression tree and returns a new ICriteria. This lets us quickly create a delegate that will call Session.CreateCriteria(string)

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			//create the new ICriteria with the current entity name, as opposed to the entity type
			var queryable = Session.Linq<TEntity>();
			queryable.QueryOptions.CreateCriteraFunction = (s, e) => s.CreateCriteria(GetEntityName());
			
			return queryable;
		}
	}

Because we are already using this property in our Find() method above, no changes are necessary, it will pick up this functionality automatically.

The changes to the NHibernate.Linq assembly are quite modest, I have included a diff in this article which you can apply to r.803 to enable this feature.

Some Gotchas

As I mentioned previously, NHibernate specifies an entity name for all entities, whether you specify one or not. If you don't, the entity name is taken from the full name of the mapped type. This means that NHibernate (currently) has no way of telling whether the entity name was explicitly specified, or taken from the class. This has an interesting side effect, which I alluded to at the start of the article, and answers the question of why you cant use a 'default' mapping with no explicit entity name.

The internals of NHibernate still have some assumptions that an entity name will be a full type name, including namespaces. The way things are currently implemented, it will examine the entity name to see if it contains a period ('.'), and if it does, it is assumed to be a class name, if it does not, it is assumed to be a user specified entity name. This means that all the existing code that expects an entity to be identified by its type will continue to work, and therefore, this behaviour is not likely to change any time soon.

So why is that important? Well, if you provide an entity name that contains a period, some sections of NHibernate (specifically SessionFactoryImpl.GetImplementors(string)) will assume it to be a type name and will start looking for all the mappings related to the persistent class. The upshot of this is that it will eventually find all of the mappings, regardless of their entity names that we defined, and use them both.

I first noticed this when I was getting an unexpected number of results in my tests, sometimes twice as many as I was expecting. The NHibernate logs showed that there were two queries being issued, one for each of the mappings, (table and view). It turned out to be the entity names I was using:

The view specific mapping used the default (that us, unspecified) entity name: "My.Namespace.TypeName"
The table specific mapping used a mangled type name: "[AllTenants] My.Namespace.TypeName"

As you can see, both of these entity names contain periods. This caused NHibernate to use both sets of mappings when performing any operation, regardless of the entity name I specified, hence the two queries being issued. The solution is to specify an explicit entity name for both mappings which contains no periods:

View specific: "My_Namspace_TypeName"
Table specific: "[AllTenants] My_Namespace_TypeName"

One downside of this approach, is that you must use the entity name in all references to the persistent class, i.e. in many-to-one and one-to-many elements. If you don't, you will get an error when you try to create the session factory complaining about a reference to an unmapped type. Remember that we are overriding the default entity name behavior with our own, so NHibernate can no longer identify an entity using its type. In my particular case, I am generating the mappings dynamically, so this extra check is not a big problem, but if you are mapping by hand or using Fluent NHibernate, its something to be aware of.

Conclusion

I've talked about mapping a single class to multiple tables (or views) using the new entity name feature in the upcoming version of NHibernate. I've also provided some suggestions on working with entity specific mappings, as well as some of the things you need to be aware of when using them. Finally, I've shown how Linq to NHibernate can be adapted for use with entity names.Doctorate Degree AND Online University Programs AND Online Certificate

The example given here, of tenant specific filtering, is perhaps not the best way to get the job done. Something more along the lines of this article may be more appropriate for a greenfield application. But if you find yourself dealing with a legacy database that exhibits this requirement, the new features in NHibernate 2.1 will allow you to do so with little or no impact on your domain architecture.Online Diploma AND Online Degree Programs

Patch for NHibernate.Linq r.803

Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs	(revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs	(working copy)
@@ -39,7 +39,12 @@
 		{
 			if (rootCriteria == null)
 			{
-				rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+				if (options.CreateCriteraFunction != null) {
+					rootCriteria = options.CreateCriteraFunction(session, expr);
+				}
+				else {
+					rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+				}
 				options.Execute(rootCriteria);
 			}
 			return expr;
Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs	(revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs	(working copy)
@@ -1,4 +1,6 @@
 using System;
+using NHibernate.Criterion;
+using NHibernate.Linq.Expressions;
 
 namespace NHibernate.Linq
 {
@@ -9,6 +11,8 @@
 	{
 		private Action<ICriteria> action;
 
+		public Func<ISession, QuerySourceExpression, ICriteria> CreateCriteraFunction;
+
 		public QueryOptions()
 		{
 			this.action = delegate { };

Mapping the same class to a view and a table using entity-name

markweee — Wed, 30 Mar 2011 11:09:39 GMT

Revision 5 posted to How to by markweee on 30/03/2011 08:09:39 a.m.

Mapping the same class to a view and a table using entity-name

Filed under: Session, Architecture, query, entity name

The Scenario

So, can this be done? Thankfully, yes, but only if you like living on the cutting edge!

Prerequisites

In this article, I'll be working against version 2.1.0.1001, revision 4099.

I'll be working against version 1.0.0.0, revision 803.

Setting up the mappings

The class we're using is fairly simple, as the magic happens in the mapping. Note that the TenantId property is nullable, as it wont be mapped when we are using the view, more on that later.


public class MyEntity {
	public virtual int Id { get; private set; }
	
	public virtual string MyProperty { get; set; }
	
	public virtual int? TenantId { get; private set; }
}


CREATE TABLE [AllItemsSchema].[MyEntity](

	[ID] int not null,

	[MyProperty] varchar(200) NULL,
	
	[TenantId] int not null,
	
	CONSTRAINT [PK_MyEntity] PRIMARY KEY CLUSTERED ([ID])
)



CREATE VIEW [TenantSpecificSchema].[MyEntity]

AS

SELECT [ID], [MyProperty] FROM [AllItemsSchema].[MyEntity] WHERE [TenantId] = dbo.GetCurrentTenant()


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="Table" schema="`AllItemsSchema`">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
		<property name="TenantId" not-null="true" />
	</class>
</hibernate-mapping>

Some things to notice here are:

The 'schema' attribute is set to 'AllItemsSchema'
The new 'entity-name' attribute is specified. In this case we are keeping it fairly simple, in the real world you would want to use something that's unique for each entity.
The TenantId property is mapped


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="View" schema="`TenantSpecificSchema`" schema-action="none">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
	</class>
</hibernate-mapping>

This is where things get interesting:

We have used the same table and class name, but notice that the 'entity-name' is different
We have a different database schema 'TenantSpecificSchema'
The TenantId property is absent as the view does not provide this
The new 'schema-action' is set to none, this will prevent NHibernate from including this mapping in its schema export, it would otherwise attempt to create a table for this view

Entity name and the ISession


public enum EntityNameMode {
	Default,
	Table,
	View
}

public class NHibernateRepository<TEntity, TKey> : IRepository<TEntity, TKey> {
	public NHibernateRepository(ISession session, EntityNameMode mode) {
		this.session = session;
		this.mode = mode;
	}
	
	public TEntity Get(TKey key) {
		return (TEntity)session.Get(GetEntityName(), key);
	}
	
	public IList<TEntity> List() {
		return session.CreateCriteria(GetEntityName()).List<TEntity>();
	}
	
	public void SaveOrUpdate(TEntity entity) {
		session.SaveOrUpdate(GetEntityName(), entity);
	}
	
	private string GetEntityName() {
		switch (mode) {
			case EntityNameMode.Table: return "Table";
			case EntityNameMode.View: return "View";
			default: return typeof(TEntity).FullName;
		}
	}
	
	private ISession session;
	private EntityNameMode mode;
}

	
	//this repository will work with data for all tenants
	var allTenantsRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.Table);

	//this repository will work with data for the current tenant only
	var currentTenantRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.View);

Using Entity Name with Linq to NHibernate

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			return session.Linq<TEntity>();
		}
	}

	//the rest of the repository is exactly the same...

	
	public TEntity Find(Expression<Func<TEntity, bool>> predicate) {
		return Linq.Where(predicate).FirstOrDefault();
	}

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			//create the new ICriteria with the current entity name, as opposed to the entity type
			var queryable = Session.Linq<TEntity>();
			queryable.QueryOptions.CreateCriteraFunction = (s, e) => s.CreateCriteria(GetEntityName());
			
			return queryable;
		}
	}

Because we are already using this property in our Find() method above, no changes are necessary, it will pick up this functionality automatically.

The changes to the NHibernate.Linq assembly are quite modest, I have included a diff in this article which you can apply to r.803 to enable this feature.

Some Gotchas

The view specific mapping used the default (that us, unspecified) entity name: "My.Namespace.TypeName"
The table specific mapping used a mangled type name: "[AllTenants] My.Namespace.TypeName"

View specific: "My_Namspace_TypeName"
Table specific: "[AllTenants] My_Namespace_TypeName"

Conclusion

I've talked about mapping a single class to multiple tables (or views) using the new entity name feature in the upcoming version of NHibernate. I've also provided some suggestions on working with entity specific mappings, as well as some of the things you need to be aware of when using them. Finally, I've shown how Linq to NHibernate can be adapted for use with entity names. Doctorate Degree AND Online University Programs AND Online Certificate

Patch for NHibernate.Linq r.803

Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs	(revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs	(working copy)
@@ -39,7 +39,12 @@
 		{
 			if (rootCriteria == null)
 			{
-				rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+				if (options.CreateCriteraFunction != null) {
+					rootCriteria = options.CreateCriteraFunction(session, expr);
+				}
+				else {
+					rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+				}
 				options.Execute(rootCriteria);
 			}
 			return expr;
Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs	(revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs	(working copy)
@@ -1,4 +1,6 @@
 using System;
+using NHibernate.Criterion;
+using NHibernate.Linq.Expressions;
 
 namespace NHibernate.Linq
 {
@@ -9,6 +11,8 @@
 	{
 		private Action<ICriteria> action;
 
+		public Func<ISession, QuerySourceExpression, ICriteria> CreateCriteraFunction;
+
 		public QueryOptions()
 		{
 			this.action = delegate { };

Mapping the same class to a view and a table using entity-name

Robert Byrne — Fri, 27 Feb 2009 20:37:38 GMT

Revision 4 posted to How to by Robert Byrne on 27/02/2009 05:37:38 p.m.

Mapping the same class to a view and a table using entity-name

Filed under: Session, Architecture, query, entity name

The Scenario

You have a single class which you must map to both a table and a database view (or perhaps another table). The view is returning records from the table itself, usually filtered, and the view may have more or less columns than the table. A more practical example is a multi tenant database, where a table has a tenant column, and the view filters the records to show only the ones associated with the current tenant. In this case, the backing table has a tenant column, but the view doesn't. To make things even more interesting, the table is in a separate database schema. For more details on this multi tenant architectural pattern see this article. Other possible uses are for this mapping technique include dynamically mapping the same base class to multiple subclass tables, which is described here,

You want to map this in NHibernate, in a way that will allow you to specify which 'representation' of the entity you want to see, either the table containing records for all tenants, or the view containing records for the currently active tenant. Why? Perhaps your system needs to access all the records for all tenants to perform auditing or cleanup, things like that. In all other cases, you only want to show the records filtered for the current tenant, via the mapped view.

So, can this be done? Thankfully, yes, but only if you like living on the cutting edge!

Prerequisites

In this article, I'll be working against version 2.1.0.1001, revision 4099.

I'll be working against version 1.0.0.0, revision 803.

Setting up the mappings

The class we're using is fairly simple, as the magic happens in the mapping. Note that the TenantId property is nullable, as it wont be mapped when we are using the view, more on that later.


public class MyEntity {
	public virtual int Id { get; private set; }
	
	public virtual string MyProperty { get; set; }
	
	public virtual int? TenantId { get; private set; }
}


CREATE TABLE [TableSchema]AllItemsSchema].[MyEntity](

	[ID] int not null,

	[MyProperty] varchar(200) NULL,
	
	[TenantId] int not null,
	
	CONSTRAINT [PK_MyEntity] PRIMARY KEY CLUSTERED ([ID])
)



CREATE VIEW [dbo]TenantSpecificSchema].[MyEntity]

AS

SELECT [ID], [MyProperty] FROM [TableSchema]AllItemsSchema].[MyEntity] WHERE [TenantId] = dbo.GetCurrentTenant()


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="Table" schema="`TableSchema`AllItemsSchema`">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
		<property name="TenantId" not-null="true" />
	</class>
</hibernate-mapping>

Some things to notice here are:

The 'schema' attribute is set to 'TableSchemaAllItemsSchema'
The new 'entity-name' attribute is specified. In this case we are keeping it fairly simple, in the real world you would want to use something that's unique for each entity.
The TenantId property is mapped


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="View" schema="`dbo`TenantSpecificSchema`" schema-action="none">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
	</class>
</hibernate-mapping>

This is where things get interesting:

We have used the same table and class name, but notice that the 'entity-name' is different
We have a different database schema 'TenantSpecificSchema'
The TenantId property is absent as the view does not provide this
The new 'schema-action' is set to none, this will prevent NHibernate from including this mapping in its schema export, it would otherwise attempt to create a table for this view

Now that we have the mappings we can spin up a session factory using your favourite favorite technique. Because we have used entity names for both of our mappings, you will see that we cant just store and retrieve entities by their type as usual. The entities are no longer identified by their types, but their entity name instead. Initially, I had planned to specify the entity name only for one of the mappings, and leave the other mapping as a 'default' with just its [Type] 'name' specified, but as I will explain later in more detail, this wont work as expected. If you want to reliably use entity name on one mapping of the class, you must use an entity name on them all.

Entity name and the ISession


public enum EntityNameMode {
	Default,
	Table,
	View
}

public class NHibernateRepository<TEntity, TKey> : IRepository<TEntity, TKey> {
	public NHibernateRepository(ISession session, EntityNameMode mode) {
		this.session = session;
		this.mode = mode;
	}
	
	public TEntity Get(TKey key) {
		return (TEntity)session.Get(GetEntityName(), key);
	}
	
	public IList<TEntity> List() {
		return session.CreateCriteria(GetEntityName()).List<TEntity>();
	}
	
	public void SaveOrUpdate(TEntity entity) {
		session.SaveOrUpdate(GetEntityName(), entity);
	}
	
	private string GetEntityName() {
		switch (mode) {
			case EntityNameMode.Table: return "Table";
			case EntityNameMode.View: return "View";
			default: return typeof(TEntity).FullName;
		}
	}
	
	private ISession session;
	private EntityNameMode mode;
}

	
	//this repository will work with data for all tenants
	var allTenantsRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.Table);

	//this repository will work with data for the current tenant only
	var currentTenantRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.View);

Using Entity Name with Linq to NHibernate

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			return session.Linq<TEntity>();
		}
	}

	//the rest of the repository is exactly the same...

	
	public TEntity Find(Expression<Func<TEntity, bool>> predicate) {
		return Linq.Where(predicate).FirstOrDefault();
	}

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			//create the new ICriteria with the current entity name, as opposed to the entity type
			var queryable = Session.Linq<TEntity>();
			queryable.QueryOptions.CreateCriteraFunction = (s, e) => s.CreateCriteria(GetEntityName());
			
			return queryable;
		}
	}

Because we are already using this property in our Find() method above, no changes are necessary, it will pick up this functionality automatically.

The changes to the NHibernate.Linq assembly are quite modest, I have included a diff in this article which you can apply to r.803 to enable this feature.

Some Gotchas

The view specific mapping used the default (that us, unspecified) entity name: "My.Namespace.TypeName"
The table specific mapping used a mangled type name: "[AllTenants] My.Namespace.TypeName"

View specific: "My_Namspace_TypeName"
Table specific: "[AllTenants] My_Namespace_TypeName"

Conclusion

Patch for NHibernate.Linq r.803

Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs	(revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs	(working copy)
@@ -39,7 +39,12 @@
 		{
 			if (rootCriteria == null)
 			{
-				rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+				if (options.CreateCriteraFunction != null) {
+					rootCriteria = options.CreateCriteraFunction(session, expr);
+				}
+				else {
+					rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+				}
 				options.Execute(rootCriteria);
 			}
 			return expr;
Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs	(revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs	(working copy)
@@ -1,4 +1,6 @@
 using System;
+using NHibernate.Criterion;
+using NHibernate.Linq.Expressions;
 
 namespace NHibernate.Linq
 {
@@ -9,6 +11,8 @@
 	{
 		private Action<ICriteria> action;
 
+		public Func<ISession, QuerySourceExpression, ICriteria> CreateCriteraFunction;
+
 		public QueryOptions()
 		{
 			this.action = delegate { };

Mapping the same class to a view and a table using entity-name

Robert Byrne — Fri, 27 Feb 2009 19:47:00 GMT

Revision 3 posted to How to by Robert Byrne on 27/02/2009 04:47:00 p.m.

Mapping the same class to a view and a table using entity-name

The Scenario

You have a single class which you must map to both a table and a database view (or perhaps another table). The view is returning records from the table itself, usually filtered, and the view may have more or less columns than the table. A more practical example is a multi tenant database, where a table has a tenant column, and the view filters the records to show only the ones associated with the current tenant. In this case, the backing table has a tenant column, but the view doesn't. To make things even more interesting, the table is in a separate database schema. Other possible uses are dynamically mapping the same base class to multiple subclass tables, which is described here,

You want to map this in NHibernate, in a way that will allow you to specify which 'representation' of the entity you want to see, either the table containing records for all tenants, or the view containing records for the currently active tenant. Why? Perhaps your system needs to access all the records for all tenants to perform auditing or cleanup, things like that. In all other cases, you only want to show the records for the current tenant, via the mapped view.

So, can this be done? Thankfully, yes, but only if you like living on the cutting edge!

Prerequisites

In this article, I'll be working against version 2.1.0.1001, revision 4099.

I'll be working against version 1.0.0.0, revision 803.

Setting up the mappings

The class we're using is fairly simple, as the magic happens in the mapping. Note that the TenantId property is nullable, as it wont be mapped when we are using the view, more on that later.


public class MyEntity {
	public virtual int Id { get; private set; }
	
	public virtual string MyProperty { get; set; }
	
	public virtual int? TenantId { get; private set; }
}


CREATE TABLE [TableSchema].[MyEntity](

	[ID] int not null,

	[MyProperty] varchar(200) NULL,
	
	[TenantId] int not null,
	
	CONSTRAINT [PK_MyEntity] PRIMARY KEY CLUSTERED ([ID])
)



CREATE VIEW [dbo].[MyEntity]

AS

SELECT [ID], [MyProperty] FROM [TableSchema].[MyEntity] WHERE [TenantId] = dbo.GetCurrentTenant()


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="Table" schema="`TableSchema`">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
		<property name="TenantId" not-null="true" />
	</class>
</hibernate-mapping>

Some things to notice here are:

The 'schema' attribute is set to 'TableSchema'
The new 'entity-name' attribute is specified. In this case we are keeping it fairly simple, in the real world you would want to use something that's unique for each entity.
The TenantId property is mapped


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="View" schema="`dbo`" schema-action="none">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
	</class>
</hibernate-mapping>

This is where things get interesting:

We have used the same table and class name, but notice that the 'entity-name' is different
We have a different database schema
The TenantId property is absent as the view does not provide this
The new 'schema-action' is set to none, this will prevent NHibernate from including this mapping in its schema export, it would otherwise attempt to create a table for this view

Now that we have the mappings we can spin up a session factory using your favourite technique. Because we have used entity names for both of our mappings, you will see that we cant just store and retrieve entities by their type as usual. The entities are no longer identified by their types, but their entity name instead. Initially, I had planned to specify the entity name only for one of the mappings, and leave the other mapping as a 'default' with just its [Type] 'name' specified, but as I will explain later in more detail, this wont work as expected. If you want to reliably use entity name on one mapping of the class, you must use an entity name on them all.

Entity name and the ISession


public enum EntityNameMode {
	Default,
	Table,
	View
}

public class NHibernateRepository<TEntity, TKey> : IRepository<TEntity, TKey> {
	public NHibernateRepository(ISession session, EntityNameMode mode) {
		this.session = session;
		this.mode = mode;
	}
	
	public TEntity Get(TKey key) {
		return (TEntity)session.Get(GetEntityName(), key);
	}
	
	public IList<TEntity> List() {
		return session.CreateCriteria(GetEntityName()).List<TEntity>();
	}
	
	public void SaveOrUpdate(TEntity entity) {
		session.SaveOrUpdate(GetEntityName(), entity);
	}
	
	private string GetEntityName() {
		switch (mode) {
			case EntityNameMode.Table: return "Table";
			case EntityNameMode.View: return "View";
			default: return typeof(TEntity).FullName;
		}
	}
	
	private ISession session;
	private EntityNameMode mode;
}

	
	//this repository will work with data for all tenants
	var allTenantsRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.Table);

	//this repository will work with data for the current tenant only
	var currentTenantRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.View);

Using Entity Name with Linq to NHibernate

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			return session.Linq<TEntity>();
		}
	}

	//the rest of the repository is exactly the same...

	
	public TEntity Find(Expression<Func<TEntity, bool>> predicate) {
		return Linq.Where(predicate).FirstOrDefault();
	}

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			//create the new ICriteria with the current entity name, as opposed to the entity type
			var queryable = Session.Linq<TEntity>();
			queryable.QueryOptions.CreateCriteraFunction = (s, e) => s.CreateCriteria(GetEntityName());
			
			return queryable;
		}
	}

Because we are already using this property in our Find() method above, no changes are necessary, it will pick up this functionality automatically.

The changes to the NHibernate.Linq assembly are quite modest, I have included a diff in this article which you can apply to r.803 to enable this feature.

Some Gotchas

The view specific mapping used the default (that us, unspecified) entity name: "My.Namespace.TypeName"
The table specific mapping used a mangled type name: "[AllTenants] My.Namespace.TypeName"

View specific: "My_Namspace_TypeName"
Table specific: "[AllTenants] My_Namespace_TypeName"

Conclusion

Patch for NHibernate.Linq r.803

Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs (revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs (working copy)
@@ -39,7 +39,12 @@
{
if (rootCriteria == null)
{
- rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+ if (options.CreateCriteraFunction != null) {
+ rootCriteria = options.CreateCriteraFunction(session, expr);
+ }
+ else {
+ rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+ }
options.Execute(rootCriteria);
}
return expr;
Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs (revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs (working copy)
@@ -1,4 +1,6 @@
using System;
+using NHibernate.Criterion;
+using NHibernate.Linq.Expressions;

namespace NHibernate.Linq
{
@@ -9,6 +11,8 @@
{
private Action<ICriteria> action;

+ public Func<ISession, QuerySourceExpression, ICriteria> CreateCriteraFunction;
+
public QueryOptions()
{
this.action = delegate { };

Mapping the same class to a view and a table using entity-name

Robert Byrne — Fri, 27 Feb 2009 19:38:18 GMT

Revision 2 posted to How to by Robert Byrne on 27/02/2009 04:38:18 p.m.

Mapping the same class to a view and a table using entity-name

The Scenario

You have a single class which you must map to both a table and a database view (or perhaps another table). The view is returning records from the table itself, usually filtered, and the view may have more or less columns than the table. A more practical example is a multi tenant database, where a table has a tenant column, and the view filters the records to show only the ones associated with the current tenant. In this case, the backing table has a tenant column, but the view doesn't. To make things even more interesting, the table is in a separate database schema. Other possible uses are dynamically mapping the same base class to multiple subclass tables, which is described here,

You want to map this in NHibernate, in a way that will allow you to specify which 'representation' of the entity you want to see, either the table containing records for all tenants, or the view containing records for the currently active tenant. Why? Perhaps your system needs to access all the records for all tenants to perform auditing or cleanup, things like that. In all other cases, you only want to show the records for the current tenant, via the mapped view.

So, can this be done? Thankfully, yes, but only if you like living on the cutting edge!

Prerequisites

In this article, I'll be working against version 2.1.0.1001, revision 4099.

I'll be working against version 1.0.0.0, revision 803.

Setting up the mappings

The class we're using is fairly simple, as the magic happens in the mapping. Note that the TenantId property is nullable, as it wont be mapped when we are using the view, more on that later.


public class MyEntity {
	public virtual int Id { get; private set; }
	
	public virtual string MyProperty { get; set; }
	
	public virtual int? TenantId { get; private set; }
}


CREATE TABLE [TableSchema].[MyEntity](

	[ID] int not null,

	[MyProperty] varchar(200) NULL,
	
	[TenantId] int not null,
	
	CONSTRAINT [PK_MyEntity] PRIMARY KEY CLUSTERED ([ID])
)



CREATE VIEW [dbo].[MyEntity]

AS

SELECT [ID], [MyProperty] FROM [TableSchema].[MyEntity] WHERE [TenantId] = dbo.GetCurrentTenant()


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="Table" schema="`TableSchema`">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
		<property name="TenantId" not-null="true" />
	</class>
</hibernate-mapping>

Some things to notice here are:

The 'schema' attribute is set to 'TableSchema'
The new 'entity-name' attribute is specified. In this case we are keeping it fairly simple, in the real world you would want to use something that's unique for each entity.
The TenantId property is mapped


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="View" schema="`dbo`" schema-action="none">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
	</class>
</hibernate-mapping>

This is where things get interesting:

We have used the same table and class name, but notice that the 'entity-name' is different
We have a different database schema
The TenantId property is absent as the view does not provide this
The new 'schema-action' is set to none, this will prevent NHibernate from including this mapping in its schema export, it would otherwise attempt to create a table for this view

Entity name and the ISession


public enum EntityNameMode {
	Default,
	Table,
	View
}

public class NHibernateRepository<TEntity, TKey> : IRepository<TEntity, TKey> {
	public NHibernateRepository(ISession session, EntityNameMode mode) {
		this.session = session;
		this.mode = mode;
	}
	
	public TEntity Get(TKey key) {
		return (TEntity)session.Get(GetEntityName(), key);
	}
	
	public IList<TEntity> List() {
		return session.CreateCriteria(GetEntityName()).List<TEntity>();
	}
	
	public void SaveOrUpdate(TEntity entity) {
		session.SaveOrUpdate(GetEntityName(), entity);
	}
	
	private string GetEntityName() {
		switch (mode) {
			case EntityNameMode.Table: return "Table";
			case EntityNameMode.View: return "View";
			default: return typeof(TEntity).FullName;
		}
	}
	
	private ISession session;
	private EntityNameMode mode;
}

	
	//this repository will work with data for all tenants
	var allTenantsRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.Table);

	//this repository will work with data for the current tenant only
	var currentTenantRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.View);

Using Entity Name with Linq to NHibernate

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			return session.Linq<TEntity>();
		}
	}

	//the rest of the repository is exactly the same...

	
	public TEntity Find(Expression<Func<TEntity, bool>> predicate) {
		return Linq.Where(predicate).FirstOrDefault();
	}

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			//create the new ICriteria with the current entity name, as opposed to the entity type
			var queryable = Session.Linq<TEntity>();
			queryable.QueryOptions.CreateCriteraFunction = (s, e) => s.CreateCriteria(GetEntityName());
			
			return queryable;
		}
	}

Because we are already using this property in our Find() method above, no changes are necessary, it will pick up this functionality automatically.

The changes to the NHibernate.Linq assembly are quite modest, I have included a diff in this article which you can apply to r.803 to enable this feature.

Some Gotchas

The view specific mapping used the default (that us, unspecified) entity name: "My.Namespace.TypeName"
The table specific mapping used a mangled type name: "[AllTenants] My.Namespace.TypeName"

View specific: "My_Namspace_TypeName"
Table specific: "[AllTenants] My_Namespace_TypeName"

Conclusion

Patch for NHibernate.Linq r.803

Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs (revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs (working copy)
@@ -39,7 +39,12 @@
{
if (rootCriteria == null)
{
- rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+ if (options.CreateCriteraFunction != null) {
+ rootCriteria = options.CreateCriteraFunction(session, expr);
+ }
+ else {
+ rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+ }
options.Execute(rootCriteria);
}
return expr;
Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs (revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs (working copy)
@@ -1,4 +1,6 @@
using System;
+using NHibernate.Criterion;
+using NHibernate.Linq.Expressions;

namespace NHibernate.Linq
{
@@ -9,6 +11,8 @@
{
private Action<ICriteria> action;

+ public Func<ISession, QuerySourceExpression, ICriteria> CreateCriteraFunction;
+
public QueryOptions()
{
this.action = delegate { };

Mapping the same class to a view and a table using entity-name

Robert Byrne — Fri, 27 Feb 2009 19:36:21 GMT

Revision 1 posted to How to by Robert Byrne on 27/02/2009 04:36:21 p.m.

The Scenario

You have a single class which you must map to both a table and a database view (or perhaps another table). The view is returning records from the table itself, usually filtered, and the view may have more or less columns than the table. A more practical example is a multi tenant database, where a table has a tenant column, and the view filters the records to show only the ones associated with the current tenant. In this case, the backing table has a tenant column, but the view doesn't. To make things even more interesting, the table is in a separate database schema. Other possible uses are dynamically mapping the same base class to multiple subclass tables, which is described here,

You want to map this in NHibernate, in a way that will allow you to specify which 'representation' of the entity you want to see, either the table containing records for all tenants, or the view containing records for the currently active tenant. Why? Perhaps your system needs to access all the records for all tenants to perform auditing or cleanup, things like that. In all other cases, you only want to show the records for the current tenant, via the mapped view.

So, can this be done? Thankfully, yes, but only if you like living on the cutting edge!

Prerequisites

In this article, I'll be working against version 2.1.0.1001, revision 4099.

I'll be working against version 1.0.0.0, revision 803.

Setting up the mappings

The class we're using is fairly simple, as the magic happens in the mapping. Note that the TenantId property is nullable, as it wont be mapped when we are using the view, more on that later.


public class MyEntity {
	public virtual int Id { get; private set; }
	
	public virtual string MyProperty { get; set; }
	
	public virtual int? TenantId { get; private set; }
}


CREATE TABLE [TableSchema].[MyEntity](

	[ID] int not null,

	[MyProperty] varchar(200) NULL,
	
	[TenantId] int not null,
	
	CONSTRAINT [PK_MyEntity] PRIMARY KEY CLUSTERED ([ID])
)



CREATE VIEW [dbo].[MyEntity]

AS

SELECT [ID], [MyProperty] FROM [TableSchema].[MyEntity] WHERE [TenantId] = dbo.GetCurrentTenant()


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="Table" schema="`TableSchema`">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
		<property name="TenantId" not-null="true" />
	</class>
</hibernate-mapping>

Some things to notice here are:

The 'schema' attribute is set to 'TableSchema'
The new 'entity-name' attribute is specified. In this case we are keeping it fairly simple, in the real world you would want to use something that's unique for each entity.
The TenantId property is mapped


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="MyAssembly" namespace="MyAssembly.MyNamespace">
	<class name="MyEntity" table="`MyEntity`" entity-name="View" schema="`dbo`" schema-action="none">
		<id name="Id">
			<generator class="native" />
		</id>
		<property name="MyProperty" length="200" />
	</class>
</hibernate-mapping>

This is where things get interesting:

We have used the same table and class name, but notice that the 'entity-name' is different
We have a different database schema
The TenantId property is absent as the view does not provide this
The new 'schema-action' is set to none, this will prevent NHibernate from including this mapping in its schema export, it would otherwise attempt to create a table for this view

Entity name and the ISession


public enum EntityNameMode {
	Default,
	Table,
	View
}

public class NHibernateRepository<TEntity, TKey> : IRepository<TEntity, TKey> {
	public NHibernateRepository(ISession session, EntityNameMode mode) {
		this.session = session;
		this.mode = mode;
	}
	
	public TEntity Get(TKey key) {
		return (TEntity)session.Get(GetEntityName(), key);
	}
	
	public IList<TEntity> List() {
		return session.CreateCriteria(GetEntityName()).List<TEntity>();
	}
	
	public void SaveOrUpdate(TEntity entity) {
		session.SaveOrUpdate(GetEntityName(), entity);
	}
	
	private string GetEntityName() {
		switch (mode) {
			case EntityNameMode.Table: return "Table";
			case EntityNameMode.View: return "View";
			default: return typeof(TEntity).FullName;
		}
	}
	
	private ISession session;
	private EntityNameMode mode;
}

	
	//this repository will work with data for all tenants
	var allTenantsRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.Table);

	//this repository will work with data for the current tenant only
	var currentTenantRepository = new NHibernateRepository<MyEntity, int>(session, EntityNameMode.View);

Using Entity Name with Linq to NHibernate

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			return session.Linq<TEntity>();
		}
	}

	//the rest of the repository is exactly the same...

	
	public TEntity Find(Expression<Func<TEntity, bool>> predicate) {
		return Linq.Where(predicate).FirstOrDefault();
	}

	
	protected INHibernateQueryable<TEntity> Linq {
		get {
			//create the new ICriteria with the current entity name, as opposed to the entity type
			var queryable = Session.Linq<TEntity>();
			queryable.QueryOptions.CreateCriteraFunction = (s, e) => s.CreateCriteria(GetEntityName());
			
			return queryable;
		}
	}

Because we are already using this property in our Find() method above, no changes are necessary, it will pick up this functionality automatically.

The changes to the NHibernate.Linq assembly are quite modest, I have included a diff in this article which you can apply to r.803 to enable this feature.

Some Gotchas

The view specific mapping used the default (that us, unspecified) entity name: "My.Namespace.TypeName"
The table specific mapping used a mangled type name: "[AllTenants] My.Namespace.TypeName"

View specific: "My_Namspace_TypeName"
Table specific: "[AllTenants] My_Namespace_TypeName"

Conclusion

Patch for NHibernate.Linq r.803

Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs (revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/Visitors/NHibernateQueryTranslator.cs (working copy)
@@ -39,7 +39,12 @@
{
if (rootCriteria == null)
{
- rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+ if (options.CreateCriteraFunction != null) {
+ rootCriteria = options.CreateCriteraFunction(session, expr);
+ }
+ else {
+ rootCriteria = session.CreateCriteria(expr.ElementType, expr.Alias);
+ }
options.Execute(rootCriteria);
}
return expr;
Index: trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs
===================================================================
--- trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs (revision 803)
+++ trunk/src/NHibernate.Linq/src/NHibernate.Linq/QueryOptions.cs (working copy)
@@ -1,4 +1,6 @@
using System;
+using NHibernate.Criterion;
+using NHibernate.Linq.Expressions;

namespace NHibernate.Linq
{
@@ -9,6 +11,8 @@
{
private Action<ICriteria> action;

+ public Func<ISession, QuerySourceExpression, ICriteria> CreateCriteraFunction;
+
public QueryOptions()
{
this.action = delegate { };

Creating an Audit Log using NHibernate Events

John Davidson — Thu, 08 Sep 2011 00:01:26 GMT

Current revision posted to How to by John Davidson on 07/09/2011 09:01:26 p.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate.

Options

There are a number of ways of doing this, using IInterceptor or the NHibernate 2.0 Event model. As the event model is fairly new, there isn't a lot of information or examples about how to use it therefore most examples deal with IInterceptor.The Audit logging itself can be recorded via multiple tables per class, single table to cover all classes, track all changes, track latest changes etc.

Solution

This solution uses the Event model, a single table for all classes and track latest change only. It also depends on the database key being a GUID, not an integer. When a class is deleted, the audit information is also removed. This might not be appropriate for your scenario.

Background

The solution operates within a repository pattern (nielson, Domain Driven Design) design where there is a single repository wrapping the NHibernate Session. This repository exposes an Interface that is defined in the business layer that the NHibernate Repository implements. Therefore the repository depends on the domain, not the domain depends on the repository. An IoC product (Spring.NET, Unity etc.) is used to wire these together.

The Domain has no reference to anything to do with NHibernate but, to ease development; each business entity inherits from the abstract Entity class and implements the IEntity interface. It is the Entity class that tracks the audit information for the business class that inherits from it.

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary domain.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

public Entity()
{
_id = Guid.Empty;
_version = new byte[8];
_createdBy = string.IsNullOrEmpty(Thread.CurrentPrincipal.Identity.Name) ? UnknownUser : Thread.CurrentPrincipal.Identity.Name;
_createdTimestamp = DateTime.Now;
_entityName = this.GetType().FullName;
}
}

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

<?xml version="1.0" encoding="utf-8"?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="Sample.Domain" assembly="Sample.Domain" default-access="field.camelcase-underscore" default-lazy="true">
<class name="Task" proxy="Sample.Domain.Interfaces.ITask, Sample.Domain.Interfaces" table="Task">
<id name="Id" column="Id" unsaved-value="00000000-0000-0000-0000-000000000000" access="property">
<generator class="guid.comb" />
</id>
<version name="Version" column="Version" type="binary" unsaved-value="null" generated="always"/>

Implementation

From the mapping we can see that the Task class uses an Interface (ITask) for its proxy generation (though virtual methods are just as acceptable) but more importantly that the Task class is populated from a join between the Audit table and the Task table. The join column is the Entity ID which, like the Id in the task table is a GUID. As GUID's are almost guaranteed to be unique there is very little likelihood of the being a key collision between the Task table and (e.g.) a Group table each storing their ID in the same column. Unfortunatley this is not the case for a HiLo key generation mechanism.

Therefore this Join element is telling NHibernate to do a SQL join on the Id of the primary table (Task) with the Entity ID of the Audit table. In effect, its the same as multi table inheritence but without the inheritence.

The power of this is that Nhibernate automatically keeps the two tables in line... an add to Task results in two SQL inserts (Task and Audit), a delete of Task results in two deletes etc. If you wish to retain audit information, but not the business data, in the case of a delete then this solution is not for you, though you could consider the "pre-delete" event to deal with retaining the audit information somehow.

Wiring into the NHibernate Event model

The NHibernate 2.0 Event model can be implemented a number of ways, inherit from a base class or implement an interface. This solution uses an interface as it allows a single listener class to deal with both updates and inserts.

The best events to use for Auditing in this scenario are "pre-update" and "pre-insert". First we write a listener class that implements two interfaces IPreUpdateEventListener and IPreInsertEventListener. This class needs to ensure that the "state" of the object to be written is updated prior to NHibernate writing out the class information. Unfortunately this state information is held in a string array and cannot be accessed in a TypeSafe manner.

internal class AuditEventListener : IPreUpdateEventListener, IPreInsertEventListener
{
public bool OnPreUpdate(PreUpdateEvent e)
{
UpdateAuditTrail(e.State, e.Persister.PropertyNames, (IEntity)e.Entity);
return false;
}
public bool OnPreInsert(PreInsertEvent e)
{
UpdateAuditTrail(e.State, e.Persister.PropertyNames, (IEntity)e.Entity);
return false;
}
private void UpdateAuditTrail(object[] state, string[] names, IEntity entity)
{
var idx = Array.FindIndex(names, n => n == "UpdatedBy");
state[idx] = string.IsNullOrEmpty(Thread.CurrentPrincipal.Identity.Name) ? "Unknown" : Thread.CurrentPrincipal.Identity.Name;
entity.UpdatedBy = state[idx].ToString();
idx = Array.FindIndex(names, n => n == "UpdatedTimestamp");
DateTime now = DateTime.Now;
state[idx] = now;
entity.UpdatedTimestamp = now;
}
}

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

So now when an object is written (the presumption is that all objects written implement the business IEntity interface) Nhibernate will run the listener, find the audit properties in the current NHibernate State and update them.To ensure the object itself also has the latest values, we update the entity instance as well.

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

This article works great, thanks Graham. I just wanted to point out there is an NHibernate gotcha/ feature related to using the OnPre* events with inheritance which is documented further on this WIKI post.

Creating an Audit Log using NHibernate Events

John Davidson — Wed, 13 Jul 2011 10:56:41 GMT

Revision 33 posted to How to by John Davidson on 13/07/2011 07:56:41 a.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate.

Options

Solution

Background

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary domain.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping iPad 3 rumors file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

iPad 3 rumors — Wed, 13 Jul 2011 06:13:14 GMT

Revision 32 posted to How to by iPad 3 rumors on 13/07/2011 03:13:14 a.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate.

Options

Solution

Background

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary domain

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping iPad 3 rumors file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

domain — Wed, 13 Jul 2011 04:15:56 GMT

Revision 31 posted to How to by domain on 13/07/2011 01:15:56 a.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate.

Options

Solution

Background

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.domain

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

Compare Telephone Service — Tue, 12 Jul 2011 17:48:11 GMT

Revision 30 posted to How to by Compare Telephone Service on 12/07/2011 02:48:11 p.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate.

Options

Solution

Background

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

John Davidson — Mon, 11 Jul 2011 10:50:23 GMT

Revision 29 posted to How to by John Davidson on 11/07/2011 07:50:23 a.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernatehosted voip.

Options

Solution

Background

The Domain has no reference car battery chargers to anything to do with NHibernate but, to ease development; each business entity inherits from the abstract Entity class and implements the IEntity interface. It is the Entity class that tracks the audit information for the business class that inherits from it.

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

Scott Findlater — Mon, 11 Jul 2011 07:45:25 GMT

Revision 28 posted to How to by Scott Findlater on 11/07/2011 04:45:25 a.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate hosted voip.

Options

Solution

Background

these together.

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

hosted voip — Mon, 11 Jul 2011 07:26:33 GMT

Revision 27 posted to How to by hosted voip on 11/07/2011 04:26:33 a.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate hosted voip.

Options

Solution

Background

these together.

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

web sitesi — Mon, 11 Jul 2011 05:05:31 GMT

Revision 26 posted to How to by web sitesi on 11/07/2011 02:05:31 a.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate.

Options

Solution

Background

these together.

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

web sitesi — Mon, 11 Jul 2011 05:04:56 GMT

Revision 25 posted to How to by web sitesi on 11/07/2011 02:04:56 a.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate.

Options

Solution

Background

web sitesi

these together.

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

Health Insurance Claim Denials — Fri, 08 Jul 2011 15:26:53 GMT

Revision 24 posted to How to by Health Insurance Claim Denials on 08/07/2011 12:26:53 p.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate.

Options

Solution

Background

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

car battery chargers — Tue, 05 Jul 2011 16:11:22 GMT

Revision 23 posted to How to by car battery chargers on 05/07/2011 01:11:22 p.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate.

Options

Solution

Background

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

John Davidson — Tue, 05 Jul 2011 10:49:14 GMT

Revision 22 posted to How to by John Davidson on 05/07/2011 07:49:14 a.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestampGreek Subs. You want this do be done automatically by NHibernate.

Options

Solution

This solution uses the Event model, a single Potenzmittel table for all classes and track latest change only. It also depends on the database key being a GUID, not an integer. When a class is deleted, the audit information is also removed. This might not be appropriate for your scenario.

Background

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

The power of this is that Nhibernate automatically keeps Computer Repair the two tables in line... an add to Task results in two SQL inserts (Task and Audit), a delete of Task results in two deletes etc. If you wish to retain audit information, but not the business data, in the case of a delete then this solution is not for you, though you could consider the "pre-delete" event to deal with retaining the audit information somehow.

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

Greek Subs — Tue, 05 Jul 2011 04:45:31 GMT

Revision 21 posted to How to by Greek Subs on 05/07/2011 01:45:31 a.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp Greek Subs. You want this do be done automatically by NHibernate.

Options

Solution

Background

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

Computer Repair — Tue, 05 Jul 2011 03:29:19 GMT

Revision 20 posted to How to by Computer Repair on 05/07/2011 12:29:19 a.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate.

Options

Solution

Background

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Creating an Audit Log using NHibernate Events

Potenzmittel — Tue, 05 Jul 2011 02:14:53 GMT

Revision 19 posted to How to by Potenzmittel on 04/07/2011 11:14:53 p.m.

Creating an Audit Log using NHibernate Events

Filed under: Audit, log, events

Scenario

You want to create an audit table so that changes to business entities are tracked with a timestamp. You want this do be done automatically by NHibernate.

Options

Solution

Background

Entity Id's are GUID's as opposed to integers. The entity Id maps to the database primary key.

Classes

The abstract Entity class is as follows

[Serializable]
public abstract class Entity : IEntity
{
private const string UnknownUser = "Unknown";

private Guid _id;
private byte[] _version;
private DateTime _createdTimestamp;
private string _createdBy;
private DateTime _updatedTimestamp;
private string _updatedBy;

[Snip: Property declarations removed for brevity]

Each business class extends this however is appropriate.

Mappings

An example mapping file for a class that extends the entity class might be:

Implementation

Wiring into the NHibernate Event model

Don't ask me why we return false in the implemented methods.... I'm not sure yet, but it works :)

Hooking NHibernate into the Listener

This is the easy bit - add the following to the hibernate.cfg.xml file (within the SessionFactory element) and you're done!

A Side Note

Retrieve a nested component with Criteria API

John Davidson — Tue, 23 Aug 2011 11:38:17 GMT

Current revision posted to How to by John Davidson on 23/08/2011 08:38:17 a.m.

Retrieve a nested component with Criteria API

Filed under: Mapping, Projections, Criteria API, Component

Sometimes it may be necessary to retrieve a nested component type of a class. NHibernate does not provide any direct solution for this, and the most obvious aproach using a projection does not work.

Using regular HQL it is possible to retrieve a component, but in more advanced situations it can be a pain concatenating HQL strings to perform a task.

What we will be accomplishing is this:

Let's assume we have an entity called Foo. Foo has a nested component called Bar. Bar is mapped using <component> in the mapping file for Foo.

To return only Bar from Foo with id 12 we'd write something similar to this using HQL:

public Bar GetBarFromFooById(int id)
{
    var query = CurrentSession.CreateQuery("select f.Bar from Foo f where f.Id = :id");
    query.SetParameter("id", id);
    return query.UniqueResult<Bar>();
}

The above code is pretty simple, and is pretty useful. However, when things becomes a bit more complex it can be really ugly, like this:

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var hql = "select f.Bar from foo"; 
    var parameters = new Dictionary<string, object>();
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        hql += " where f.Baz = :bazValue";
        parameters.Add("bazValue", bazValue);
    }
 
    if (fooId.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Id = :fooId";
        parameters.Add("fooId", fooId.Value);
    }
 
    if (mustHaveProperty.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Bar.TheProperty = :mustHaveProperty";
        parameters.Add("mustHaveProperty", mustHaveProperty.Value);
    }
 
 
    var query = CurrentSession.CreateQuery(hql);
 
    foreach (var parameter in parameters)
    {
        query.SetParameter(parameter.Key, parameter.Value);
    }
 
    return query.UniqueResult<Bar>();
}

As you can see, the above, not so unrealistic, example makes it pretty difficult to work with HQL in a very dynamic way. Fortunately the Criteria API is very flexible in this regards, but is missing a couple of features only supported in HQL. In the real world you'd probably come up with some smart mutators for the string etc. but this was just to prove a point.

The example above could be written like the following using the Criteria API (although it won't work, it serves as an example to support the actual solution):

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var criteria = CurrentSession.CreateCriteria(typeof(Foo), "f");
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        criteria.Add(Restrictions.Eq("f.Baz", bazValue));
    }
 
    if (fooId.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Id", fooId.Value));
    }
 
    if (mustHaveProperty.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Bar.TheProperty", mustHaveProperty.Value));
    }
 
    criteria.SetProjection(Projections.Property("f.Bar"));
    criteria.SetResultTransformer(Transformers.AliasToBean(typeof(Bar)));
 
    return criteria.UniqueResult<Bar>();
}

The example above will throw a runtime exception because the projection does not map to a single property. Of course this makes sense in the absolute most strict way as Bar is not a simple property. The point, however, is that the Criteria API makes it much easier to work with dynamic queries and it is very powerful.

Since there is no built-in support (that I know of that is) for this type of projection, the only way is to manually do the mapping using a projectionlist.Graduate Certificate AND Undergraduate Diploma AND Online Schools

One way to do this would be to create a static class containing the projectionlist like this:

internal static class MyProjections
{
    public static IProjection Bar
    {
        get
        {
            return Projections.ProjectionList()
                .Add(Projections.Property("Bar.Property1"), "Property1")
                .Add(Projections.Property("Bar.TheProperty"), "TheProperty")
                .Add(Projections.Property("Bar.AnotherProperty"), "AnotherProperty");
        }
    }
}

With the projectionlist in place, it's simply a question of using this in the example above like this:

criteria.SetProjection(MyProjections.Bar);Graduate
 Diploma AND Phd
Degree

Now we can return the mapped component class. Of course the projection is not safe in a deeper nesting, but this could be solved by making a projection factory or something similar. i recently started automated forex trading and the results so far have been great, i highly recommend it to anyone!Online Degree AND Bachelor Degree

Very well said, I think that if everyone thinks this way that the world would be a much better place.. especially if my cash out refinance gets approved! Distance Learning AND Affordable Degree AND Education Degree

Retrieve a nested component with Criteria API

John Davidson — Tue, 23 Aug 2011 11:30:36 GMT

Revision 7 posted to How to by John Davidson on 23/08/2011 08:30:36 a.m.

Retrieve a nested component with Criteria API

Filed under: Mapping, Projections, Criteria API, Component

Sometimes it may be necessary to retrieve a nested component type of a class. NHibernate does not provide any direct solution for this, and the most obvious aproach using a projection does not work.

Using regular HQL it is possible to retrieve a component, but in more advanced situations it can be a pain concatenating HQL strings to perform a task math help with probability.

What we will be accomplishing is this:

Let's assume we have an entity called Foo. Foo has a nested component called Bar. Bar is mapped using <component> in the mapping file for Foo.

To return only Bar from Foo with id 12 we'd write something similar to this using HQL:

public Bar GetBarFromFooById(int id)
{
    var query = CurrentSession.CreateQuery("select f.Bar from Foo f where f.Id = :id");
    query.SetParameter("id", id);
    return query.UniqueResult<Bar>();
}

The above code is pretty simple, and is pretty useful. However, when things becomes a bit more complex it can be really ugly, like this:

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var hql = "select f.Bar from foo"; 
    var parameters = new Dictionary<string, object>();
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        hql += " where f.Baz = :bazValue";
        parameters.Add("bazValue", bazValue);
    }
 
    if (fooId.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Id = :fooId";
        parameters.Add("fooId", fooId.Value);
    }
 
    if (mustHaveProperty.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Bar.TheProperty = :mustHaveProperty";
        parameters.Add("mustHaveProperty", mustHaveProperty.Value);
    }
 
 
    var query = CurrentSession.CreateQuery(hql);
 
    foreach (var parameter in parameters)
    {
        query.SetParameter(parameter.Key, parameter.Value);
    }
 
    return query.UniqueResult<Bar>();
}

The example above could be written like the following using the Criteria API (although it won't work, it serves as an example to support the actual solution):

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var criteria = CurrentSession.CreateCriteria(typeof(Foo), "f");
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        criteria.Add(Restrictions.Eq("f.Baz", bazValue));
    }
 
    if (fooId.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Id", fooId.Value));
    }
 
    if (mustHaveProperty.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Bar.TheProperty", mustHaveProperty.Value));
    }
 
    criteria.SetProjection(Projections.Property("f.Bar"));
    criteria.SetResultTransformer(Transformers.AliasToBean(typeof(Bar)));
 
    return criteria.UniqueResult<Bar>();
}

Since there is no built-in support (that I know of that is) for this type of projection, the only way is to manually do the mapping using a projectionlist. Graduate Certificate AND Undergraduate Diploma AND Online Schools

One way to do this would be to create a static class containing the projectionlist like this:

internal static class MyProjections
{
    public static IProjection Bar
    {
        get
        {
            return Projections.ProjectionList()
                .Add(Projections.Property("Bar.Property1"), "Property1")
                .Add(Projections.Property("Bar.TheProperty"), "TheProperty")
                .Add(Projections.Property("Bar.AnotherProperty"), "AnotherProperty");
        }
    }
}

With the projectionlist in place, it's simply a question of using this in the example above like this:

criteria.SetProjection(MyProjections.Bar); Graduate
 Diploma AND Phd
Degree

Retrieve a nested component with Criteria API

piter — Tue, 23 Aug 2011 08:57:14 GMT

Revision 6 posted to How to by piter on 23/08/2011 05:57:14 a.m.

Retrieve a nested component with Criteria API

Filed under: Mapping, Projections, Criteria API, Component

Sometimes it may be necessary to retrieve a nested component type of a class. NHibernate does not provide any direct solution for this, and the most obvious aproach using a projection does not work.

Using regular HQL it is possible to retrieve a component, but in more advanced situations it can be a pain concatenating HQL strings to perform a task math help with probability.

What we will be accomplishing is this:

Let's assume we have an entity called Foo. Foo has a nested component called Bar. Bar is mapped using <component> in the mapping file for Foo.

To return only Bar from Foo with id 12 we'd write something similar to this using HQL:

public Bar GetBarFromFooById(int id)
{
    var query = CurrentSession.CreateQuery("select f.Bar from Foo f where f.Id = :id");
    query.SetParameter("id", id);
    return query.UniqueResult<Bar>();
}

The above code is pretty simple, and is pretty useful. However, when things becomes a bit more complex it can be really ugly, like this:

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var hql = "select f.Bar from foo"; 
    var parameters = new Dictionary<string, object>();
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        hql += " where f.Baz = :bazValue";
        parameters.Add("bazValue", bazValue);
    }
 
    if (fooId.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Id = :fooId";
        parameters.Add("fooId", fooId.Value);
    }
 
    if (mustHaveProperty.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Bar.TheProperty = :mustHaveProperty";
        parameters.Add("mustHaveProperty", mustHaveProperty.Value);
    }
 
 
    var query = CurrentSession.CreateQuery(hql);
 
    foreach (var parameter in parameters)
    {
        query.SetParameter(parameter.Key, parameter.Value);
    }
 
    return query.UniqueResult<Bar>();
}

The example above could be written like the following using the Criteria API (although it won't work, it serves as an example to support the actual solution):

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var criteria = CurrentSession.CreateCriteria(typeof(Foo), "f");
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        criteria.Add(Restrictions.Eq("f.Baz", bazValue));
    }
 
    if (fooId.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Id", fooId.Value));
    }
 
    if (mustHaveProperty.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Bar.TheProperty", mustHaveProperty.Value));
    }
 
    criteria.SetProjection(Projections.Property("f.Bar"));
    criteria.SetResultTransformer(Transformers.AliasToBean(typeof(Bar)));
 
    return criteria.UniqueResult<Bar>();
}

Since there is no built-in support (that I know of that is) for this type of projection, the only way is to manually do the mapping using a projectionlist. Graduate Certificate AND Undergraduate Diploma AND Online Schools

One way to do this would be to create a static class containing the projectionlist like this:

internal static class MyProjections
{
    public static IProjection Bar
    {
        get
        {
            return Projections.ProjectionList()
                .Add(Projections.Property("Bar.Property1"), "Property1")
                .Add(Projections.Property("Bar.TheProperty"), "TheProperty")
                .Add(Projections.Property("Bar.AnotherProperty"), "AnotherProperty");
        }
    }
}

With the projectionlist in place, it's simply a question of using this in the example above like this:

criteria.SetProjection(MyProjections.Bar); Graduate
 Diploma AND Phd
Degree

Retrieve a nested component with Criteria API

markweee — Wed, 30 Mar 2011 11:04:24 GMT

Revision 5 posted to How to by markweee on 30/03/2011 08:04:24 a.m.

Retrieve a nested component with Criteria API

Filed under: Mapping, Projections, Criteria API, Component

Sometimes it may be necessary to retrieve a nested component type of a class. NHibernate does not provide any direct solution for this, and the most obvious aproach using a projection does not work.

Using regular HQL it is possible to retrieve a component, but in more advanced situations it can be a pain concatenating HQL strings to perform a task.

What we will be accomplishing is this:

Let's assume we have an entity called Foo. Foo has a nested component called Bar. Bar is mapped using <component> in the mapping file for Foo.

To return only Bar from Foo with id 12 we'd write something similar to this using HQL:

public Bar GetBarFromFooById(int id)
{
    var query = CurrentSession.CreateQuery("select f.Bar from Foo f where f.Id = :id");
    query.SetParameter("id", id);
    return query.UniqueResult<Bar>();
}

The above code is pretty simple, and is pretty useful. However, when things becomes a bit more complex it can be really ugly, like this:

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var hql = "select f.Bar from foo"; 
    var parameters = new Dictionary<string, object>();
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        hql += " where f.Baz = :bazValue";
        parameters.Add("bazValue", bazValue);
    }
 
    if (fooId.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Id = :fooId";
        parameters.Add("fooId", fooId.Value);
    }
 
    if (mustHaveProperty.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Bar.TheProperty = :mustHaveProperty";
        parameters.Add("mustHaveProperty", mustHaveProperty.Value);
    }
 
 
    var query = CurrentSession.CreateQuery(hql);
 
    foreach (var parameter in parameters)
    {
        query.SetParameter(parameter.Key, parameter.Value);
    }
 
    return query.UniqueResult<Bar>();
}

The example above could be written like the following using the Criteria API (although it won't work, it serves as an example to support the actual solution):

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var criteria = CurrentSession.CreateCriteria(typeof(Foo), "f");
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        criteria.Add(Restrictions.Eq("f.Baz", bazValue));
    }
 
    if (fooId.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Id", fooId.Value));
    }
 
    if (mustHaveProperty.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Bar.TheProperty", mustHaveProperty.Value));
    }
 
    criteria.SetProjection(Projections.Property("f.Bar"));
    criteria.SetResultTransformer(Transformers.AliasToBean(typeof(Bar)));
 
    return criteria.UniqueResult<Bar>();
}

Since there is no built-in support (that I know of that is) for this type of projection, the only way is to manually do the mapping using a projectionlist. Graduate Certificate AND Undergraduate Diploma AND Online Schools

One way to do this would be to create a static class containing the projectionlist like this:

internal static class MyProjections
{
    public static IProjection Bar
    {
        get
        {
            return Projections.ProjectionList()
                .Add(Projections.Property("Bar.Property1"), "Property1")
                .Add(Projections.Property("Bar.TheProperty"), "TheProperty")
                .Add(Projections.Property("Bar.AnotherProperty"), "AnotherProperty");
        }
    }
}

With the projectionlist in place, it's simply a question of using this in the example above like this:

criteria.SetProjection(MyProjections.Bar); Graduate
 Diploma AND Phd
Degree

Retrieve a nested component with Criteria API

markweee — Wed, 30 Mar 2011 10:50:11 GMT

Revision 4 posted to How to by markweee on 30/03/2011 07:50:11 a.m.

Retrieve a nested component with Criteria API

Filed under: Mapping, Projections, Criteria API, Component

Sometimes it may be necessary to retrieve a nested component type of a class. NHibernate does not provide any direct solution for this, and the most obvious aproach using a projection does not work.

Using regular HQL it is possible to retrieve a component, but in more advanced situations it can be a pain concatenating HQL strings to perform a task.

What we will be accomplishing is this:

Let's assume we have an entity called Foo. Foo has a nested component called Bar. Bar is mapped using <component> in the mapping file for Foo.

To return only Bar from Foo with id 12 we'd write something similar to this using HQL:

public Bar GetBarFromFooById(int id)
{
    var query = CurrentSession.CreateQuery("select f.Bar from Foo f where f.Id = :id");
    query.SetParameter("id", id);
    return query.UniqueResult<Bar>();
}

The above code is pretty simple, and is pretty useful. However, when things becomes a bit more complex it can be really ugly, like this:

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var hql = "select f.Bar from foo"; 
    var parameters = new Dictionary<string, object>();
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        hql += " where f.Baz = :bazValue";
        parameters.Add("bazValue", bazValue);
    }
 
    if (fooId.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Id = :fooId";
        parameters.Add("fooId", fooId.Value);
    }
 
    if (mustHaveProperty.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Bar.TheProperty = :mustHaveProperty";
        parameters.Add("mustHaveProperty", mustHaveProperty.Value);
    }
 
 
    var query = CurrentSession.CreateQuery(hql);
 
    foreach (var parameter in parameters)
    {
        query.SetParameter(parameter.Key, parameter.Value);
    }
 
    return query.UniqueResult<Bar>();
}

The example above could be written like the following using the Criteria API (although it won't work, it serves as an example to support the actual solution):

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var criteria = CurrentSession.CreateCriteria(typeof(Foo), "f");
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        criteria.Add(Restrictions.Eq("f.Baz", bazValue));
    }
 
    if (fooId.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Id", fooId.Value));
    }
 
    if (mustHaveProperty.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Bar.TheProperty", mustHaveProperty.Value));
    }
 
    criteria.SetProjection(Projections.Property("f.Bar"));
    criteria.SetResultTransformer(Transformers.AliasToBean(typeof(Bar)));
 
    return criteria.UniqueResult<Bar>();
}

Since there is no built-in support (that I know of that is) for this type of projection, the only way is to manually do the mapping using a projectionlist.

One way to do this would be to create a static class containing the projectionlist like this:

internal static class MyProjections
{
    public static IProjection Bar
    {
        get
        {
            return Projections.ProjectionList()
                .Add(Projections.Property("Bar.Property1"), "Property1")
                .Add(Projections.Property("Bar.TheProperty"), "TheProperty")
                .Add(Projections.Property("Bar.AnotherProperty"), "AnotherProperty");
        }
    }
}

With the projectionlist in place, it's simply a question of using this in the example above like this:

criteria.SetProjection(MyProjections.Bar);

Retrieve a nested component with Criteria API

markweee — Wed, 30 Mar 2011 10:49:28 GMT

Revision 3 posted to How to by markweee on 30/03/2011 07:49:28 a.m.

Retrieve a nested component with Criteria API

Filed under: Mapping, Projections, Criteria API, Component

Sometimes it may be necessary to retrieve a nested component type of a class. NHibernate does not provide any direct solution for this, and the most obvious aproach using a projection does not work.

Using regular HQL it is possible to retrieve a component, but in more advanced situations it can be a pain concatenating HQL strings to perform a task.

What we will be accomplishing is this:

Let's assume we have an entity called Foo. Foo has a nested component called Bar. Bar is mapped using <component> in the mapping file for Foo.

To return only Bar from Foo with id 12 we'd write something similar to this using HQL:

public Bar GetBarFromFooById(int id)
{
    var query = CurrentSession.CreateQuery("select f.Bar from Foo f where f.Id = :id");
    query.SetParameter("id", id);
    return query.UniqueResult<Bar>();
}

The above code is pretty simple, and is pretty useful. However, when things becomes a bit more complex it can be really ugly, like this:

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var hql = "select f.Bar from foo"; 
    var parameters = new Dictionary<string, object>();
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        hql += " where f.Baz = :bazValue";
        parameters.Add("bazValue", bazValue);
    }
 
    if (fooId.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Id = :fooId";
        parameters.Add("fooId", fooId.Value);
    }
 
    if (mustHaveProperty.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Bar.TheProperty = :mustHaveProperty";
        parameters.Add("mustHaveProperty", mustHaveProperty.Value);
    }
 
 
    var query = CurrentSession.CreateQuery(hql);
 
    foreach (var parameter in parameters)
    {
        query.SetParameter(parameter.Key, parameter.Value);
    }
 
    return query.UniqueResult<Bar>();
}

The example above could be written like the following using the Criteria API (although it won't work, it serves as an example to support the actual solution):

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var criteria = CurrentSession.CreateCriteria(typeof(Foo), "f");
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        criteria.Add(Restrictions.Eq("f.Baz", bazValue));
    }
 
    if (fooId.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Id", fooId.Value));
    }
 
    if (mustHaveProperty.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Bar.TheProperty", mustHaveProperty.Value));
    }
 
    criteria.SetProjection(Projections.Property("f.Bar"));
    criteria.SetResultTransformer(Transformers.AliasToBean(typeof(Bar)));
 
    return criteria.UniqueResult<Bar>();
}

Since there is no built-in support (that I know of that is) for this type of projection, the only way is to manually do the mapping using a projectionlist.

One way to do this would be to create a static class containing the projectionlist like this:

internal static class MyProjections
{
    public static IProjection Bar
    {
        get
        {
            return Projections.ProjectionList()
                .Add(Projections.Property("Bar.Property1"), "Property1")
                .Add(Projections.Property("Bar.TheProperty"), "TheProperty")
                .Add(Projections.Property("Bar.AnotherProperty"), "AnotherProperty");
        }
    }
}

With the projectionlist in place, it's simply a question of using this in the example above like this:

criteria.SetProjection(MyProjections.Bar);

Retrieve a nested component with Criteria API

Kenneth Siewers Møller — Tue, 31 Mar 2009 22:50:34 GMT

Revision 2 posted to How to by Kenneth Siewers Møller on 31/03/2009 07:50:34 p.m.

Retrieving Retrieve a nested component with Criteria API

Filed under: Mapping, Projections, Criteria API, Component

Sometimes it may be necessary to retrieve a nested component type of a class. NHibernate does not provide any direct solution for this, and the most obvious aproach using a projection does not work.

Using regular HQL it is possible to retrieve a component, but in more advanced situations it can be a pain concatenating HQL strings to perform a task.

What we will be accomplishing is this:

Let's assume we have an entity called Foo. Foo has a nested component called Bar. Bar is mapped using <component> in the mapping file for Foo.

To return only Bar from Foo with id 12 we'd write something similar to this using HQL:

public Bar GetBarFromFooById(int id)
{
    var query = CurrentSession.CreateQuery("select f.Bar from Foo f where f.Id = :id");
    query.SetParameter("id", id);
    return query.UniqueResult<Bar>();
}

The above code is pretty simple, and is pretty useful. However, when things becomes a bit more complex it can be really ugly, like this:

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var hql = "select f.Bar from foo"; 
    var parameters = new Dictionary<string, object>();
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        hql += " where f.Baz = :bazValue";
        parameters.Add("bazValue", bazValue);
    }
 
    if (fooId.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Id = :fooId";
        parameters.Add("fooId", fooId.Value);
    }
 
    if (mustHaveProperty.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Bar.TheProperty = :mustHaveProperty";
        parameters.Add("mustHaveProperty", mustHaveProperty.Value);
    }
 
 
    var query = CurrentSession.CreateQuery(hql);
 
    foreach (var parameter in parameters)
    {
        query.SetParameter(parameter.Key, parameter.Value);
    }
 
    return query.UniqueResult<Bar>();
}

The example above could be written like the following using the Criteria API (although it won't work, it serves as an example to support the actual solution):

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var criteria = CurrentSession.CreateCriteria(typeof(Foo), "f");
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        criteria.Add(Restrictions.Eq("f.Baz", bazValue));
    }
 
    if (fooId.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Id", fooId.Value));
    }
 
    if (mustHaveProperty.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Bar.TheProperty", mustHaveProperty.Value));
    }
 
    criteria.SetProjection(Projections.Property("f.Bar"));
    criteria.SetResultTransformer(Transformers.AliasToBean(typeof(Bar)));
 
    return criteria.UniqueResult<Bar>();
}

Since there is no built-in support (that I know of that is) for this type of projection, the only way is to manually do the mapping using a projectionlist.

One way to do this would be to create a static class containing the projectionlist like this:

internal static class MyProjections
{
    public static IProjection Bar
    {
        get
        {
            return Projections.ProjectionList()
                .Add(Projections.Property("Bar.Property1"), "Property1")
                .Add(Projections.Property("Bar.TheProperty"), "TheProperty")
                .Add(Projections.Property("Bar.AnotherProperty"), "AnotherProperty");
        }
    }
}

With the projectionlist in place, it's simply a question of using this in the example above like this:

criteria.SetProjection(MyProjections.Bar);

Now we can return the mapped component class. Of course the projection is not safe in a deeper nesting, but this could be solved by making a projection factory or something similar.

Retrieving a nested component with Criteria API

Kenneth Siewers Møller — Wed, 11 Mar 2009 20:32:23 GMT

Revision 1 posted to How to by Kenneth Siewers Møller on 11/03/2009 05:32:23 p.m.

Sometimes it may be necessary to retrieve a nested component type of a class. NHibernate does not provide any direct solution for this, and the most obvious aproach using a projection does not work.

Using regular HQL it is possible to retrieve a component, but in more advanced situations it can be a pain concatenating HQL strings to perform a task.

What we will be accomplishing is this:

Let's assume we have an entity called Foo. Foo has a nested component called Bar. Bar is mapped using <component> in the mapping file for Foo.

To return only Bar from Foo with id 12 we'd write something similar to this using HQL:

public Bar GetBarFromFooById(int id)
{
    var query = CurrentSession.CreateQuery("select f.Bar from Foo f where f.Id = :id");
    query.SetParameter("id", id);
    return query.UniqueResult<Bar>();
}

The above code is pretty simple, and is pretty useful. However, when things becomes a bit more complex it can be really ugly, like this:

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var hql = "select f.Bar from foo"; 
    var parameters = new Dictionary<string, object>();
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        hql += " where f.Baz = :bazValue";
        parameters.Add("bazValue", bazValue);
    }
 
    if (fooId.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Id = :fooId";
        parameters.Add("fooId", fooId.Value);
    }
 
    if (mustHaveProperty.HasValue)
    {
        if (!hql.Contains("where"))
        {
            hql += " where";
        }
        else
        {
            hql += " and";
        }
 
        hql += " f.Bar.TheProperty = :mustHaveProperty";
        parameters.Add("mustHaveProperty", mustHaveProperty.Value);
    }
 
 
    var query = CurrentSession.CreateQuery(hql);
 
    foreach (var parameter in parameters)
    {
        query.SetParameter(parameter.Key, parameter.Value);
    }
 
    return query.UniqueResult<Bar>();
}

The example above could be written like the following using the Criteria API (although it won't work, it serves as an example to support the actual solution):

public Bar GetBarFromFooBySomeProperties(string bazValue, int? fooId, bool? mustHaveProperty)
{
    var criteria = CurrentSession.CreateCriteria(typeof(Foo), "f");
 
    if (!string.IsNullOrEmpty(bazValue))
    {
        criteria.Add(Restrictions.Eq("f.Baz", bazValue));
    }
 
    if (fooId.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Id", fooId.Value));
    }
 
    if (mustHaveProperty.HasValue)
    {
        criteria.Add(Restrictions.Eq("f.Bar.TheProperty", mustHaveProperty.Value));
    }
 
    criteria.SetProjection(Projections.Property("f.Bar"));
    criteria.SetResultTransformer(Transformers.AliasToBean(typeof(Bar)));
 
    return criteria.UniqueResult<Bar>();
}

Since there is no built-in support (that I know of that is) for this type of projection, the only way is to manually do the mapping using a projectionlist.

One way to do this would be to create a static class containing the projectionlist like this:

internal static class MyProjections
{
    public static IProjection Bar
    {
        get
        {
            return Projections.ProjectionList()
                .Add(Projections.Property("Bar.Property1"), "Property1")
                .Add(Projections.Property("Bar.TheProperty"), "TheProperty")
                .Add(Projections.Property("Bar.AnotherProperty"), "AnotherProperty");
        }
    }
}

With the projectionlist in place, it's simply a question of using this in the example above like this:

criteria.SetProjection(MyProjections.Bar);

Now we can return the mapped component class. Of course the projection is not safe in a deeper nesting, but this could be solved by making a projection factory or something similar.

A fully working skeleton for sexy Loquacious NH

Scott Findlater — Wed, 17 Aug 2011 22:28:41 GMT

Current revision posted to How to by Scott Findlater on 17/08/2011 07:28:41 p.m.

A fully working skeleton for sexy Loquacious NH

Filed under: Mapping by code

After spending the last few months learning NHibernate, starting with hbm xml, to Fluent NHibernate, then Loquacious sexy mapping was released.

Herewith is a solution, with tests and ioc, for a fully working skeleton demonstrating both explicit mapping by code and mapping by convention.

Domain; details the problem domain ... a small Customer, Order, Product etc domain but with all the fun relationships!!

Domain.NHByCode; is the mapping of the domain using the ModelMapper, with Explicit Mappings. Sorry Fabio, I have been very conformist here with single mapping classes ;)

Domain.NHByConvention; is the mapping of the same domain using the ConventionModelMapper.

These are the key blog posts by Fabio;

01 04 2011 - NHibernate 3.2 mapping by code; http://fabiomaulo.blogspot.com/2011/04/nhibernate-32-mapping-by-code.html
08 04 2011 - NHibernate 3.2: (part 2) mapping by code; http://fabiomaulo.blogspot.com/2011/04/nhibernate-32-part-2-mapping-by-code.html
13 04 2011 - NHibernate 3.2: mapping by code conventions; http://fabiomaulo.blogspot.com/2011/04/nhibernate-32-mapping-by-code_13.html
16 07 2011 - NHibernate: playing with mapping by code; http://fabiomaulo.blogspot.com/2011/07/nhibernate-playing-with-mapping-by-code.html
17 07 2011 - NHibernate: playing with mapping by code (2); http://fabiomaulo.blogspot.com/2011/07/nhibernate-playing-with-mapping-by-code_17.html

Other resources;

http://www.nhforge.org/doc/nh/en/index.html
http://nhforge.org/wikis/
A nice NH set vs bag answer http://stackoverflow.com/questions/1916350/set-bag-and-list-set-in-nhibernate/1921727#1921727

Grab the code here - https://github.com/ScottFindlater/Loquacious-NH

A fully working skeleton for sexy Loquacious NH

Scott Findlater — Wed, 17 Aug 2011 22:27:14 GMT

Revision 2 posted to How to by Scott Findlater on 17/08/2011 07:27:14 p.m.

A fully working skeleton for sexy Loquacious NH

Filed under: Mapping by code

After spending the last few months learning NHibernate, starting with hbm xml, to Fluent NHibernate, then Loquacious sexy mapping was released.

Herewith is a solution, with tests and ioc, for a fully working skeleton demonstrating both explicit mapping by code and mapping by convention.

Domain; details the problem domain ... a small Customer, Order, Product etc domain but with all the fun relationships!!

Domain.NHByCode; is the mapping of the domain using the ModelMapper, with Explicit Mappings. Sorry Fabio, I have been very conformist here with single mapping classes ;)

Domain.NHByConvention; is the mapping of the same domain using the ConventionModelMapper.

These are the key blog posts by Fabio; 01 04 2011 - NHibernate 3.2 mapping by code; http://fabiomaulo.blogspot.com/2011/04/nhibernate-32-mapping-by-code.html 08 04 2011 - NHibernate 3.2: (part 2) mapping by code; http://fabiomaulo.blogspot.com/2011/04/nhibernate-32-part-2-mapping-by-code.html 13 04 2011 - NHibernate 3.2: mapping by code conventions; http://fabiomaulo.blogspot.com/2011/04/nhibernate-32-mapping-by-code_13.html 16 07 2011 - NHibernate: playing with mapping by code; http://fabiomaulo.blogspot.com/2011/07/nhibernate-playing-with-mapping-by-code.html 17 07 2011 - NHibernate: playing with mapping by code (2); http://fabiomaulo.blogspot.com/2011/07/nhibernate-playing-with-mapping-by-code_17.html

Other resources; http://www.nhforge.org/doc/nh/en/index.html http://nhforge.org/wikis/ A nice NH set vs bag answer http://stackoverflow.com/questions/1916350/set-bag-and-list-set-in-nhibernate/1921727#1921727

Grab the code here - https://github.com/ScottFindlater/Loquacious-NH

A fully working skeleton for sexy Loquacious NH

Scott Findlater — Wed, 17 Aug 2011 21:20:50 GMT

Revision 1 posted to How to by Scott Findlater on 17/08/2011 06:20:50 p.m.

After spending the last few months learning NHibernate, starting with hbm xml, to Fluent NHibernate, then Loquacious sexy mapping was released.  
Herewith is a solution, with tests and ioc, for a fully working skeleton demonstrating both explicit mapping by code and mapping by convention.

Domain; details the problem domain ... a small Customer, Order, Product etc domain but with all the fun relationships!!

Domain.NHByCode; is the mapping of the domain using the ModelMapper, with Explicit Mappings.  Sorry Fabio, I have been very conformist here with single mapping classes ;)

Domain.NHByConvention; is the mapping of the same domain using the ConventionModelMapper.

These are the key blog posts by Fabio;
01 04 2011 - NHibernate 3.2 mapping by code;
http://fabiomaulo.blogspot.com/2011/04/nhibernate-32-mapping-by-code.html

08 04 2011 - NHibernate 3.2: (part 2) mapping by code;
http://fabiomaulo.blogspot.com/2011/04/nhibernate-32-part-2-mapping-by-code.html

13 04 2011 - NHibernate 3.2: mapping by code conventions;
http://fabiomaulo.blogspot.com/2011/04/nhibernate-32-mapping-by-code_13.html

16 07 2011 - NHibernate: playing with mapping by code;
http://fabiomaulo.blogspot.com/2011/07/nhibernate-playing-with-mapping-by-code.html

17 07 2011 - NHibernate: playing with mapping by code (2);
http://fabiomaulo.blogspot.com/2011/07/nhibernate-playing-with-mapping-by-code_17.html

Other resources;
http://www.nhforge.org/doc/nh/en/index.html
http://nhforge.org/wikis/
A nice NH set vs bag answer http://stackoverflow.com/questions/1916350/set-bag-and-list-set-in-nhibernate/1921727#1921727

Grab the code here - https://github.com/ScottFindlater/Loquacious-NH

.NET type generation for NHibernate mapping collections

Igor Ignatov — Tue, 09 Aug 2011 09:01:00 GMT

Current revision posted to How to by Igor Ignatov on 09/08/2011 06:01:00 a.m.

As our users might know, the Devart company has recently released a new version of Entity Developer that supports NHibernate that is intended to provide users with a powerful and convenient visual model designer for NHibernate.

When writing templates for generating entity classes for NHibernate models in Devart Entity Developer for NHibernate, I tried to understand to which .NET types in generated entity classes NHibernate collection were mapped to and in which structure they were stored. I read quite a lot of online articles on the subject, but none provided me an exhaustive answer. After I cleared up this issue, I decided to describe this aspect in an article.

So, there are the following types of collection mapping in NHibernate:

Set;
List;
Bag;
Idbag;
Map;
Array.

The Generic collection can be used in all type of NHibernate collection mapping, except for Array.

Set maps to an Iesi.Collections.ISet. The interface is part of the Iesi.Collections assembly distributed with NHibernate. The field of the class, in which the collection is stored, is initialized with an object of the Iesi.Collections.HashedSet type; it is also part of Iesi.Collections assembly distributed with NHibernate. If the collection is mapped as the generic one, Set maps to an Iesi.Collections.Generic.ISet<T>, while the field is initialized with an object of the Iesi.Collections.Generic.HashedSet<T> type, where T is the details entity.

List, Bag and Idbag map to System.Collections.IList. The field of the class, in which the collection is stored, is initialized with an object of the System.Collections.ArrayList type. When mapped as generic, the collection maps to System.Collections.Generic.IList<T>, while the field is initialized with an object of the System.Collections.Generic.List<T> type, where T is the details entity.

Map maps to System.Collections.IDictionary. The field of the class, in which the collection is stored, is initialized with an object of the System.Collections.Hashtable type. If the collection is mapped as the generic one, Map maps to System.Collections.Generic.IDictionary<TIndex, T>, while the field is initialized with an object of the System.Collections.Generic.Dictionary<TIndex, T>, where TIndex is the type of the collection index, and T is the details entity.

Array maps to an array of collection elements(T[] for C#). The field of the class, where the the collection is stored, is initialized as an array of collection elements.

The initialization of the field in the class constructor, where the collection is stores, is declarative and is performed in order to prevent the null reference exception when the property of a newly created class object is called. When data are obtained from the database and mapped to objects, NHibernate run-time re-initializes the field and fills in the collection.

Changing Values in NHibernate Events

Stefan Steinegger — Mon, 08 Aug 2011 15:20:19 GMT

Current revision posted to How to by Stefan Steinegger on 08/08/2011 12:20:19 p.m.

Changing Values in OnPreUpdate NHibernate Events

Filed under: events, listener

Abstract

Audit trails using NHibernate's event model often use the OnPreInsert and OnPreUpdate event listeners to change/ modify the state of the entity. Although It may work in some cases and is sometimes referred to as a solution, it should be noted the OnPreInsert and OnPreUpdate events are not intended to be used to change the values of the entity and instead they should be used to check values and for that reason they return "veto"

There is also a bug report about that.

Why OnPreUpdate Triggers May Fail

There is a reason for that. NHibernate does the folowing:

When flushing, the FlushEntityEventListener is called for each entity in the session.
It determines the dirty properties.
Based on the dirty properties, it determines if the entity needs updating
It calls PreUpdate triggers
Based on the dirty properties it updates the corresponding tables.

The last point is the critical one. If your PreUpdate trigger changes properties that are not found dirty before and which are not in the same table as the dirty properties, it won't be updated in the database. The same happens when dynamic-update is used.

Example:

Now, when you change Name in the session (it gets dirty) and Value in the trigger, the table AnotherTable won't be updated.

How To Implement It The Correct Way

The correct way is to use the FlushEntityEventListener to implement property changeschanges.The important difference is that you can provide a list of changed properties in this event listener, and therefore tell NHibernate what to store.

There is an example by Buthrakaur.

History

There is a solution to reproduce the code by Scott Findlater here. The tests folder in each project highlights successes/ issues (by failing tests) in each project.

Project - 01OnPreEvents. This project shows a typical, working, approach to audit trails using the OnPreInsert and OnPreUpdate to modify the entity state. An Entity base class which is inherited by a Category class. The base Entity provides identification and common auditing properties.

Project - 02OnPreEventsFailing. This project shows how an inheritance entity hierarchy using the OnPreInsert and OnPreUpdate events to modify entity state fail to persist the changed entity state. Here, for whatever design decision, the Entity base class which originally provide identification and common auditing has been split into Entity and AuditableEntity. Now the Category class inherits from AuditableEntity.

Project - 03Save. Uses the same entity inheritance hierarchy from the 02OnPreEventsFailing project to demonstrate a working version using the Save/ Insert events.

References to the problem

Audit trails using NHibernate's event model are well documented;

Ayende's NHibernate IPreUpdateEventListener & IPreInsertEventListener blog post
Graham Bunce's Creating an Audit Log using NHibernate Events on this WIKI
And most recently Jason Dentler's NHibernate 3.0 cookbook, chapter 7, Creating and changing stamping entities recipe.

There is also this NHibernate bug report - changes made in IPreInsert/UpdateEventListener are not persisted into DB on inherited classes with the resolution of "not an issue" because "pre-insert and pre-update listeners are not intended to be used to change the values of the entity. Instead they should be used to check-values (for that reason they return "veto")." (see in context)

This contradiction of intended usage regarding the changing of entity state was further discussed on this NHUser Group thread, with the same answer.

There are some discussions and blog posts related to this problem:

Changing Values in OnPreUpdate Events

Stefan Steinegger — Mon, 08 Aug 2011 15:17:25 GMT

Revision 10 posted to How to by Stefan Steinegger on 08/08/2011 12:17:25 p.m.

NHibernate, Audit trails and OnPreInsert/ Changing Values in OnPreUpdate event listeners vs Save/ Update event listenersEvents

Filed under: Audit, log, events, listener

Abstract

Audit trails using NHibernate's event model often use the OnPreInsert and OnPreUpdate event listeners to change/ modify the state of the entity. While this does works Although It may work in some cases and is widely documented sometimes referred to as a solution, it should be noted the OnPreInsert and OnPreUpdate events are not intended to be used to change the values of the entity and instead they should be used to check values and for that reason they return "veto".

Code"veto"

There is also a bug report about that.

Why OnPreUpdate Triggers May Fail

There is a reason for that. NHibernate does the folowing:

When flushing, the FlushEntityEventListener is called for each entity in the session.

It determines the dirty properties.

Based on the dirty properties, it determines if the entity needs updating

It calls PreUpdate triggers

Based on the dirty properties it updates the corresponding tables.

The full solution can last point is the critical one. If your PreUpdate trigger changes properties that are not found dirty before and which are not in the same table as the dirty properties, it won't be downloaded updated in the database. The same happens when dynamic-update is used.

Example:

<class name="Foo">
<id ...>
<property name="Name"/>
<join table="AnotherTable>
<key name="id"/>
<property name="Value"/>
</join>
</class>

Now, when you change Name in the session (it gets dirty) and Value in the trigger, the table AnotherTable won't be updated.

How To Implement It The Correct Way

The correct way is to use the FlushEntityEventListener to implement property changes. There is an example by Buthrakaur.

History

There is a solution to reproduce the code by Scott Findlater here. The tests folder in each project highlights successes/ issues (by failing tests) in each project. May I politely ask you to bear in mind the aim of this code is the issue of inheritance and they have been over simplified with auditing in mind to demonstrate inheritance issues within NHibernate ... this is not a commercial design pattern/ solution.

Project - 01OnPreEvents. This project shows a typical, working, approach to audit trails using the OnPreInsert and OnPreUpdate to modify the entity state. An Entity base class which is inherited by a Category class. The base Entity provides identification and common auditing properties.

Project - 02OnPreEventsFailing. This project shows how an inheritance entity hierarchy using the OnPreInsert and OnPreUpdate events to modify entity state fail to persist the changed entity state. Here, for whatever design decision, the Entity base class which originally provide identification and common auditing has been split into Entity and AuditableEntity. Now the Category class inherits from AuditableEntity.

Project - 03Save. Uses the same entity inheritance hierarchy from the 02OnPreEventsFailing project to demonstrate a working version using the Save/ Insert events.

History

This section is the history of arriving at this post. Please read this with the spirit of sharing and attempting to contribute

References to documentation.the problem

Audit trails using NHibernate's event model are well documented;

Ayende's NHibernate IPreUpdateEventListener & IPreInsertEventListener blog post

Graham Bunce's Creating an Audit Log using NHibernate Events on this WIKI

And most recently Jason Dentler's NHibernate 3.0 cookbook, chapter 7, Creating and changing stamping entities recipe.

And there
There is no doubt all of these solutions work using the concept of changing the state of the entity before (pre) database insertion or updating.

I adopted the OnPreInsert and OnPreUpdate approach for an auditing solution within an inheritance architected solution when I found, what I thought, was an NHibernate bug. I subsequently ended up at also this NHibernate bug report - changes made in IPreInsert/UpdateEventListener are not persisted into DB on inherited classes with the unexpected resolution of "not an issue".

The solution proposed was to use the Save/ Update event listeners, which obviously works, but the unexpected reason as to why this report was not a bug was " because "pre-insert and pre-update listeners are not intended to be used to change the values of the entity. Instead they should be used to check-values (for that reason they return "veto")." (see in context)

This contradiction of intended usage regarding the changing of entity state was further discussed on this NHUser Group thread, with the same answer.

Conclusion

I note Fabio clearly states the usage for the OnPre* events and herewith is

There are some documentation. However, from the perspective of a developer learning NHibernate, I feel this is contradicted by key NHibernate community people.

I am yet discussions and blog posts related to truly understand why, with the variety of scenarios demonstrated, this is a not considered a bug. Maybe there should be some explicit enforcing of not being able to change entity state in these OnPre* events.

A detailed example from Fabio?

There seem to be alot of cries for help but with no conclusive working examples;problem:

audit listener using IFlushEntityEventListener (continuation of NH-2596)

Bizarre error when using NHibernate, IPreInsertEventListener, Oracle, batching and sequences

Clarification on NH-2596 of PreUpdate vs OnSaveOrUpdate semantics

And Fabio delivers a blog post

http://fabiomaulo.blogspot.com/2011/05/nhibernate-bizarre-audit.html

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Scott Findlater — Thu, 12 May 2011 08:47:48 GMT
Revision 9 posted to How to by Scott Findlater on 12/05/2011 05:47:48 a.m.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Filed under: Audit, log, events, listener

Abstract

Audit trails using NHibernate's event model often use the OnPreInsert and OnPreUpdate event listeners to change/ modify the state of the entity. While this does works and is widely documented as a solution, it should be noted the OnPreInsert and OnPreUpdate events are not intended to be used to change the values of the entity and instead they should be used to check values and for that reason they return "veto".

Code

The full solution can be downloaded here. The tests folder in each project highlights successes/ issues (by failing tests) in each project. May I politely ask you to bear in mind the aim of this code is the issue of inheritance and they have been over simplified with auditing in mind to demonstrate inheritance issues within NHibernate ... this is not a commercial design pattern/ solution.

Project - 01OnPreEvents. This project shows a typical, working, approach to audit trails using the OnPreInsert and OnPreUpdate to modify the entity state. An Entity base class which is inherited by a Category class. The base Entity provides identification and common auditing properties.

Project - 02OnPreEventsFailing. This project shows how an inheritance entity hierarchy using the OnPreInsert and OnPreUpdate events to modify entity state fail to persist the changed entity state. Here, for whatever design decision, the Entity base class which originally provide identification and common auditing has been split into Entity and AuditableEntity. Now the Category class inherits from AuditableEntity.

Project - 03Save. Uses the same entity inheritance hierarchy from the 02OnPreEventsFailing project to demonstrate a working version using the Save/ Insert events.

History

This section is the history of arriving at this post. Please read this with the spirit of sharing and attempting to contribute to documentation.

Audit trails using NHibernate's event model are well documented;

Ayende's NHibernate IPreUpdateEventListener & IPreInsertEventListener blog post

Graham Bunce's Creating an Audit Log using NHibernate Events on this WIKI

And most recently Jason Dentler's NHibernate 3.0 cookbook, chapter 7, Creating and changing stamping entities recipe.

And there is no doubt all of these solutions work using the concept of changing the state of the entity before (pre) database insertion or updating.

I adopted the OnPreInsert and OnPreUpdate approach for an auditing solution within an inheritance architected solution when I found, what I thought, was an NHibernate bug. I subsequently ended up at this NHibernate bug report - changes made in IPreInsert/UpdateEventListener are not persisted into DB on inherited classes with the unexpected resolution of "not an issue".

The solution proposed was to use the Save/ Update event listeners, which obviously works, but the unexpected reason as to why this report was not a bug was because "pre-insert and pre-update listeners are not intended to be used to change the values of the entity. Instead they should be used to check-values (for that reason they return "veto")." (see in context)

This contradiction of intended usage regarding the changing of entity state was further discussed on this NHUser Group thread, with the same answer.

Conclusion

I note Fabio clearly states the usage for the OnPre* events and herewith is some documentation. However, from the perspective of a developer learning NHibernate, I feel this is contradicted by key NHibernate community people.

I am yet to truly understand why, with the variety of scenarios demonstrated, this is a not considered a bug. Maybe there should be some explicit enforcing of not being able to change entity state in these OnPre* events.

A detailed example from Fabio?

There seem to be alot of cries for help but with no conclusive working examples;

audit listener using IFlushEntityEventListener (continuation of NH-2596)

Bizarre error when using NHibernate, IPreInsertEventListener, Oracle, batching and sequences

Clarification on NH-2596 of PreUpdate vs OnSaveOrUpdate semantics

And Fabio delivers a blog post

http://fabiomaulo.blogspot.com/2011/05/nhibernate-bizarre-audit.html

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Scott Findlater — Wed, 11 May 2011 12:29:26 GMT
Revision 8 posted to How to by Scott Findlater on 11/05/2011 09:29:26 a.m.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Filed under: Audit, log, events, listener

Abstract

Audit trails using NHibernate's event model often use the OnPreInsert and OnPreUpdate event listeners to change/ modify the state of the entity. While this does works and is widely documented as a solution, it should be noted the OnPreInsert and OnPreUpdate events are not intended to be used to change the values of the entity and instead they should be used to check values and for that reason they return "veto".

Code

The full solution can be downloaded here. The tests folder in each project highlights successes/ issues (by failing tests) in each project. May I politely ask you to bear in mind the aim of this code is the issue of inheritance and they have been over simplified with auditing in mind to demonstrate inheritance issues within NHibernate ... this is not a commercial design pattern/ solution.

Project - 01OnPreEvents. This project shows a typical, working, approach to audit trails using the OnPreInsert and OnPreUpdate to modify the entity state. An Entity base class which is inherited by a Category class. The base Entity provides identification and common auditing properties.

Project - 02OnPreEventsFailing. This project shows how an inheritance entity hierarchy using the OnPreInsert and OnPreUpdate events to modify entity state fail to persist the changed entity state. Here, for whatever design decision, the Entity base class which originally provide identification and common auditing has been split into Entity and AuditableEntity. Now the Category class inherits from AuditableEntity.

Project - 03Save. Uses the same entity inheritance hierarchy from the 02OnPreEventsFailing project to demonstrate a working version using the Save/ Insert events.

History

This section is the history of arriving at this post. Please read this with the spirit of sharing and attempting to contribute to documentation.

Audit trails using NHibernate's event model are well documented;

Ayende's NHibernate IPreUpdateEventListener & IPreInsertEventListener blog post

Graham Bunce's Creating an Audit Log using NHibernate Events on this WIKI

And most recently Jason Dentler's NHibernate 3.0 cookbook, chapter 7, Creating and changing stamping entities recipe.

And there is no doubt all of these solutions work using the concept of changing the state of the entity before (pre) database insertion or updating.

I adopted the OnPreInsert and OnPreUpdate approach for an auditing solution within an inheritance architected solution when I found, what I thought, was an NHibernate bug. I subsequently ended up at this NHibernate bug report - changes made in IPreInsert/UpdateEventListener are not persisted into DB on inherited classes with the unexpected resolution of "not an issue".

The solution proposed was to use the Save/ Update event listeners, which obviously works, but the unexpected reason as to why this report was not a bug was because "pre-insert and pre-update listeners are not intended to be used to change the values of the entity. Instead they should be used to check-values (for that reason they return "veto")." (see in context)

This contradiction of intended usage regarding the changing of entity state was further discussed on this NHUser Group thread, with the same answer.

Conclusion

I note Fabio clearly states the usage for the OnPre* events and herewith is some documentation. However, from the perspective of a developer learning NHibernate, I feel this is contradicted by key NHibernate community people.

I am yet to truly understand why, with the variety of scenarios demonstrated, this is a not considered a bug. Maybe there should be some explicit enforcing of not being able to change entity state in these OnPre* events.

A detailed example from Fabio?

There seem to be alot of cries for help but with no conclusive working examples;

audit listener using IFlushEntityEventListener (continuation of NH-2596)

Bizarre error when using NHibernate, IPreInsertEventListener, Oracle, batching and sequences

Clarification on NH-2596 of PreUpdate vs OnSaveOrUpdate semantics

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Scott Findlater — Wed, 27 Apr 2011 05:32:27 GMT
Revision 7 posted to How to by Scott Findlater on 27/04/2011 02:32:27 a.m.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Filed under: Audit, log, events, listener

Abstract

Audit trails using NHibernate's event model often use the OnPreInsert and OnPreUpdate event listeners to change/ modify the state of the entity. While this does works and is widely documented as a solution, it should be noted the OnPreInsert and OnPreUpdate events are not intended to be used to change the values of the entity and instead they should be used to check values and for that reason they return "veto".

Code

The full solution can be downloaded here. The tests folder in each project highlights successes/ issues (by failing tests) in each project. May I politely ask you to bear in mind the aim of this code is the issue of inheritance and they have been over simplified with auditing in mind to demonstrate inheritance issues within NHibernate ... this is not a commercial design pattern/ solution.

Project - 01OnPreEvents. This project shows a typical, working, approach to audit trails using the OnPreInsert and OnPreUpdate to modify the entity state. An Entity base class which is inherited by a Category class. The base Entity provides identification and common auditing properties.

Project - 02OnPreEventsFailing. This project shows how an inheritance entity hierarchy using the OnPreInsert and OnPreUpdate events to modify entity state fail to persist the changed entity state. Here, for whatever design decision, the Entity base class which originally provide identification and common auditing has been split into Entity and AuditableEntity. Now the Category class inherits from AuditableEntity.

Project - 03Save. Uses the same entity inheritance hierarchy from the 02OnPreEventsFailing project to demonstrate a working version using the Save/ Insert events.

History

This section is the history of arriving at this post. Please read this with the spirit of sharing and attempting to contribute to documentation.

Audit trails using NHibernate's event model are well documented;

Ayende's NHibernate IPreUpdateEventListener & IPreInsertEventListener blog post

Graham Bunce's Creating an Audit Log using NHibernate Events on this WIKI

And most recently Jason Dentler's NHibernate 3.0 cookbook, chapter 7, Creating and changing stamping entities recipe.

And there is no doubt all of these solutions work using the concept of changing the state of the entity before (pre) database insertion or updating.

I adopted the OnPreInsert and OnPreUpdate approach for an auditing solution within an inheritance architected solution when I found, what I thought, was an NHibernate bug. I subsequently ended up at this NHibernate bug report - changes made in IPreInsert/UpdateEventListener are not persisted into DB on inherited classes with the unexpected resolution of "not an issue".

The solution proposed was to use the Save/ Update event listeners, which obviously works, but the unexpected reason as to why this report was not a bug was because "pre-insert and pre-update listeners are not intended to be used to change the values of the entity. Instead they should be used to check-values (for that reason they return "veto")." (see in context)

This contradiction of intended usage regarding the changing of entity state was further discussed on this NHUser Group thread, with the same answer.

Conclusion

I note Fabio clearly states the usage for the OnPre* events and herewith is some documentation. However, from the perspective of a developer learning NHibernate, I feel this is contradicted by key NHibernate community people.

I am yet to truly understand why, with the variety of scenarios demonstrated, this is a not considered a bug. Maybe there should be some explicit enforcing of not being able to change entity state in these OnPre* events.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Scott Findlater — Tue, 26 Apr 2011 23:42:34 GMT
Revision 6 posted to How to by Scott Findlater on 26/04/2011 08:42:34 p.m.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Filed under: Audit, log, events, listener

Abstract

Audit trails using NHibernate's event model often use the OnPreInsert and OnPreUpdate event listeners to change/ modify the state of the entity. While this does works and is widely documented as a solution, it should be noted the OnPreInsert and OnPreUpdate events are not intended to be used to change the values of the entity and instead they should be used to check values and for that reason they return "veto".

Code

The full solution can be downloaded here. The tests folder in each project highlights successes/ issues (by failing tests) in each project. May I politely ask you to bear in mind the aim of this code is the issue of inheritance and they have been over simplified with auditing in mind to demonstrate inheritance issues within NHibernate ... this is not a commercial design pattern/ solution.

Project - 01OnPreEvents. This project shows a typical, working, approach to audit trails using the OnPreInsert and OnPreUpdate to modify the entity state. An Entity base class which is inherited by a Category class. The base Entity provides identification and common auditing properties.

Project - 02OnPreEventsFailing. This project shows how an inheritance entity hierarchy using the OnPreInsert and OnPreUpdate events to modify entity state fail to persist the changed entity state. Here, for whatever design decision, the Entity base class which originally provide identification and common auditing has been split into Entity and AuditableEntity. Now the Category class inherits from AuditableEntity.

Project - 03Save. Uses the same entity inheritance hierarchy from the 02OnPreEventsFailing project to demonstrate a working version using the Save/ Insert events.

History

This section is the history of arriving at this post. Please read this with the spirit of sharing and attempting to contribute to documentation.

Audit trails using NHibernate's event model are well documented;

Ayende's NHibernate IPreUpdateEventListener & IPreInsertEventListener blog post

Graham Bunce's Creating an Audit Log using NHibernate Events on this WIKI

And most recently Jason Dentler's NHibernate 3.0 cookbook, chapter 7, Creating and changing stamping entities recipe.

And there is no doubt all of these solutions work using the concept of changing the state of the entity before (pre) database insertion or updating.

I adopted the OnPreInsert and OnPreUpdate approach for an auditing solution within an inheritance architected solution when I found, what I thought, was an NHibernate bug. I subsequently ended up at this NHibernate bug report - changes made in IPreInsert/UpdateEventListener are not persisted into DB on inherited classes with the unexpected resolution of "not an issue".

The solution proposed was to use the Save/ Update event listeners, which obviously works, but the unexpected reason as to why this report was not a bug was because "pre-insert and pre-update listeners are not intended to be used to change the values of the entity. Instead they should be used to check-values (for that reason they return "veto")." (see in context)

This contradiction of intended usage regarding the changing of entity state was further discussed on this NHUser Group thread, with the same answer.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Scott Findlater — Tue, 26 Apr 2011 23:40:44 GMT
Revision 5 posted to How to by Scott Findlater on 26/04/2011 08:40:44 p.m.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Filed under: Audit, log, events, listener

Abstract

Audit trails using NHibernate's event model often use the OnPreInsert and OnPreUpdate event listeners to change/ modify the state of the entity. While this does works and is widely documented as a solution, it should be noted the OnPreInsert and OnPreUpdate events are not intended to be used to change the values of the entity and instead they should be used to check values and for that reason they return "veto".

Code

The full solution can be downloaded here. The tests folder in each project highlights successes/ issues (by failing tests) in each project. May I politely ask you to bear in mind the aim of this code is the issue of inheritance and they have been over simplified with auditing in mind to demonstrate inheritance issues within NHibernate ... this is not a commercial design pattern/ solution.

Project - 01OnPreEvents. This project shows a typical, working, approach to audit trails using the OnPreInsert and OnPreUpdate to modify the entity state. An Entity base class which is inherited by a Category class. The base Entity provides identification and common auditing properties.

Project - 02OnPreEventsFailing. This project shows how an inheritance entity hierarchy using the OnPreInsert and OnPreUpdate events to modify entity state fail to persist the changed entity state. Here, for whatever design decision, the Entity base class which originally provide identification and common auditing has been split into Entity and AuditableEntity. Now the Category class inherits from AuditableEntity.

Project - 03Save. Uses the same entity inheritance hierarchy from the 02OnPreEventsFailing project to demonstrate a working version using the Save/ Insert events.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Scott Findlater — Tue, 26 Apr 2011 23:40:12 GMT
Revision 4 posted to How to by Scott Findlater on 26/04/2011 08:40:12 p.m.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Filed under: Audit, log, events, listener

Abstract

Audit trails using NHibernate's event model often use the OnPreInsert and OnPreUpdate event listeners to change/ modify the state of the entity. While this does works and is widely documented as a solution, it should be noted the OnPreInsert and OnPreUpdate events are not intended to be used to change the values of the entity and instead they should be used to check values and for that reason they return "veto".

Code

The full solution can be downloaded here. The tests folder in each project highlights successes/ issues (by failing tests) in each project. May I politely ask you to bear in mind the aim of this code is the issue of inheritance and they have been over simplified with auditing in mind to demonstrate inheritance issues within NHibernate ... this is not a commercial design pattern/ solution.

Project - 01OnPreEvents. This project shows a typical, working, approach to audit trails using the OnPreInsert and OnPreUpdate to modify the entity state. An Entity base class which is inherited by a Category class. The base Entity provides identification and common auditing properties.

Project - 02OnPreEventsFailing. This project shows how an inheritance entity hierarchy using the OnPreInsert and OnPreUpdate events to modify entity state fail to persist the changed entity state. Here, for whatever design decision, the Entity base class which originally provide identification and common auditing has been split into Entity and AuditableEntity. Now the Category class inherits from AuditableEntity.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Scott Findlater — Tue, 26 Apr 2011 23:39:37 GMT
Revision 3 posted to How to by Scott Findlater on 26/04/2011 08:39:37 p.m.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Filed under: Audit, log, events, listener

Abstract

Audit trails using NHibernate's event model often use the OnPreInsert and OnPreUpdate event listeners to change/ modify the state of the entity. While this does works and is widely documented as a solution, it should be noted the OnPreInsert and OnPreUpdate events are not intended to be used to change the values of the entity and instead they should be used to check values and for that reason they return "veto".

Code

The full solution can be downloaded here. The tests folder in each project highlights successes/ issues (by failing tests) in each project. May I politely ask you to bear in mind the aim of this code is the issue of inheritance and they have been over simplified with auditing in mind to demonstrate inheritance issues within NHibernate ... this is not a commercial design pattern/ solution.

Project - 01OnPreEvents. This project shows a typical, working, approach to audit trails using the OnPreInsert and OnPreUpdate to modify the entity state. An Entity base class which is inherited by a Category class. The base Entity provides identification and common auditing properties.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Scott Findlater — Tue, 26 Apr 2011 23:37:53 GMT
Revision 2 posted to How to by Scott Findlater on 26/04/2011 08:37:53 p.m.

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Filed under: Audit, log, events, listener

Abstract

Audit trails using NHibernate's event model often use the OnPreInsert and OnPreUpdate event listeners to change/ modify the state of the entity. While this does works and is widely documented as a solution, it should be noted the OnPreInsert and OnPreUpdate events are not intended to be used to change the values of the entity and instead they should be used to check values and for that reason they return "veto".

NHibernate, Audit trails and OnPreInsert/ OnPreUpdate event listeners vs Save/ Update event listeners

Scott Findlater — Tue, 26 Apr 2011 23:37:53 GMT
Revision 1 posted to How to by Scott Findlater on 26/04/2011 08:37:53 p.m.

Abstract

Audit trails using NHibernate's event model often use the OnPreInsert and OnPreUpdate event listeners to change/ modify the state of the entity. While this does works and is widely documented as a solution, it should be noted the OnPreInsert and OnPreUpdate events are not intended to be used to change the values of the entity and instead they should be used to check values and for that reason they return "veto".

View the xml generated when mapping by code

rippo — Tue, 26 Jul 2011 12:42:55 GMT
Current revision posted to How to by rippo on 26/07/2011 09:42:55 a.m.

View the xml generated when mapping by code

Filed under: Architecture, Mapping by code

When using mapping by code it may not be 100% obvious what XML is being generated for NHibernate. You have a couple of options, the first option is to tell NHibernate to write all your mappings into the bin folder:-

var mapper = new ModelMapper(); mapper.AddMappings(typeof(CmsMeta).Assembly.GetTypes()); //This will write all the XML into the bin/mappings folder mapper.CompileMappingForEachExplicitlyAddedEntity().WriteAllXmlMapping();

The second option is to use the extension method .AsString(). However you will be presented with one large XML blob.

var mapper = new ModelMapper(); mapper.AddMappings(typeof(CmsMeta).Assembly.GetTypes()); var mapping = mapper.CompileMappingForAllExplicitlyAddedEntities(); //you could add a breakpoint here! var mappingXml = mapping.AsString();

Either way you will be able to quickly and easily view the XML that is being injected into NHibernate. This is very useful for debugging or if you are upgrading all your hbm.xml files into the new mapping by code syntax and wish to compare like for like.

View the xml generated when mapping by code

rippo — Tue, 26 Jul 2011 12:42:55 GMT
Revision 1 posted to How to by rippo on 26/07/2011 09:42:55 a.m.

When using mapping by code it may not be 100% obvious what XML is being generated for NHibernate. You have a couple of options, the first option is to tell NHibernate to write all your mappings into the bin folder:-

var mapper = new ModelMapper(); mapper.AddMappings(typeof(CmsMeta).Assembly.GetTypes()); //This will write all the XML into the bin/mappings folder mapper.CompileMappingForEachExplicitlyAddedEntity().WriteAllXmlMapping();

The second option is to use the extension method .AsString(). However you will be presented with one large XML blob.

var mapper = new ModelMapper(); mapper.AddMappings(typeof(CmsMeta).Assembly.GetTypes()); var mapping = mapper.CompileMappingForAllExplicitlyAddedEntities(); //you could add a breakpoint here! var mappingXml = mapping.AsString();

Either way you will be able to quickly and easily view the XML that is being injected into NHibernate. This is very useful for debugging or if you are upgrading all your hbm.xml files into the new mapping by code syntax and wish to compare like for like.

ConventionModelMapper - change ManyToOne column name

ashern — Thu, 14 Jul 2011 05:37:37 GMT
Current revision posted to How to by ashern on 14/07/2011 02:37:37 a.m.

ConventionModelMapper - change ManyToOne column name

Creating a convention to override the default column naming for your ManyToOne relationships is simple, as follows:

mapper.BeforeMapManyToOne += (insp, prop, map) =>

map.Column(prop.LocalMember.GetPropertyOrFieldType().Name + "Id");

But, if any of the above are bi-directional relationships, be sure to equivalently map the inverse side's key as required for your collection types:

for set

mapper.BeforeMapSet += (insp, typ, map) => map.Key(km => km.Column(typ.GetContainerEntity(insp).Name + "Id"))> map.Key(km =>

km.Column(typ.GetContainerEntity(insp).Name + "Id"));

for bag

mapper.BeforeMapBag += (insp, typ, map) => map.Key(km => km.Column(typ.GetContainerEntity(insp).Name + "Id"))> map.Key(km =>

km.Column(typ.GetContainerEntity(insp).Name + "Id"));

etc...

ConventionModelMapper - change ManyToOne column name

ashern — Thu, 14 Jul 2011 05:34:54 GMT
Revision 2 posted to How to by ashern on 14/07/2011 02:34:54 a.m.

ConventionModelMapper - change ManyToOne column name

Creating a convention to override the default column naming for your ManyToOne relationships is simple, as follows:

mapper.BeforeMapManyToOne += (insp, prop, map) =>

map.Column(prop.LocalMember.<wbr />GetPropertyOrFieldType().Name

map.Column(prop.LocalMember.GetPropertyOrFieldType().Name + "Id");

But, if any of the above are bi-directional relationships, be sure to equivalently map the inverse side's key as required for your collection types:

for set

mapper.BeforeMapSet += (insp, typ, map) => map.Key(km => km.Column(typ.GetContainerEntity(insp).Name + "Id"));

for bag

mapper.BeforeMapBag += (insp, typ, map) => map.Key(km => km.Column(typ.GetContainerEntity(insp).Name + "Id"));

etc...

ConventionModelMapper - change ManyToOne column name

ashern — Thu, 14 Jul 2011 05:34:07 GMT
Revision 1 posted to How to by ashern on 14/07/2011 02:34:07 a.m.

Creating a convention to override the default column naming for your ManyToOne relationships is simple, as follows:

mapper.BeforeMapManyToOne += (insp, prop, map) =>

map.Column(prop.LocalMember.<wbr />GetPropertyOrFieldType().Name + "Id");

But, if any of the above are bi-directional relationships, be sure to equivalently map the inverse side's key as required for your collection types:

for set

mapper.BeforeMapSet += (insp, typ, map) => map.Key(km => km.Column(typ.GetContainerEntity(insp).Name + "Id"));

for bag
mapper.BeforeMapBag += (insp, typ, map) => map.Key(km => km.Column(typ.GetContainerEntity(insp).Name + "Id"));

etc...

ConventionModelMapper & .net 4 ISet<>

ashern — Thu, 14 Jul 2011 05:19:16 GMT
Current revision posted to How to by ashern on 14/07/2011 02:19:16 a.m.

ConventionModelMapper & .net 4 ISet<>

For anyone using José's Net4CollectionTypeFactory to enable native ISet<> usage, here's how to get the convention mapper to recognize your ISet<> properties as type Set rather than Bag (code courtesy JFR):

In your mapping

mapper.IsSet(IsSetFieldType);

Function implementation

private static bool IsSetFieldType(MemberInfo mi, bool declared)         {             var propertyTypeIsSet = mi.GetPropertyOrFieldType()                 .GetGenericInterfaceTypeDefinitions()                 .Contains(typeof(ISet<>));             if (propertyTypeIsSet) return true;             var backFieldInfo = PropertyToField.GetBackFieldInfo((PropertyInfo)mi);             return backFieldInfo != null                    && backFieldInfo                           .FieldType.GetGenericInterfaceTypeDefinitions().Contains(typeof(ISet<>));         }

Remember to add the collection type factory to your config..

configuration.<wbr />CollectionTypeFactory<Net4CollectionTypeFactory>();

configuration.CollectionTypeFactory<Net4CollectionTypeFactory>();

ConventionModelMapper & .net 4 ISet<>

ashern — Thu, 14 Jul 2011 05:18:27 GMT
Revision 2 posted to How to by ashern on 14/07/2011 02:18:27 a.m.

ConventionModelMapper & .net 4 ISet<>

For anyone using José's Net4CollectionTypeFactory to enable native ISet<> usage, here's how to get the convention mapper to recognize your ISet<> properties as type Set rather than Bag (code courtesy JFR):

In your mapping

mapper.IsSet(IsSetFieldType);

Function implementation

private static bool IsSetFieldType(MemberInfo mi, bool declared)         {             var propertyTypeIsSet = mi.GetPropertyOrFieldType()                 .GetGenericInterfaceTypeDefinitions()                 .Contains(typeof(ISet<>));             if (propertyTypeIsSet) return true;             var backFieldInfo = PropertyToField.GetBackFieldInfo((PropertyInfo)mi);             return backFieldInfo != null                    && backFieldInfo                           .FieldType.GetGenericInterfaceTypeDefinitions().Contains(typeof(ISet<>));         }

Remember to add the collection type factory to your config..

configuration.<wbr />CollectionTypeFactory<<wbr />Net4CollectionTypeFactory>();>CollectionTypeFactory<Net4CollectionTypeFactory>();

ConventionModelMapper & .net 4 ISet<>

ashern — Thu, 14 Jul 2011 05:16:32 GMT
Revision 1 posted to How to by ashern on 14/07/2011 02:16:32 a.m.

For anyone using José's Net4CollectionTypeFactory to enable native ISet<> usage, here's how to get the convention mapper to recognize your ISet<> properties as type Set rather than Bag (code courtesy JFR):

In your mapping

mapper.IsSet(IsSetFieldType);

Function implementation

private static bool IsSetFieldType(MemberInfo mi, bool declared)         {             var propertyTypeIsSet = mi.GetPropertyOrFieldType()                 .GetGenericInterfaceTypeDefinitions()                 .Contains(typeof(ISet<>));             if (propertyTypeIsSet) return true;             var backFieldInfo = PropertyToField.GetBackFieldInfo((PropertyInfo)mi);             return backFieldInfo != null                    && backFieldInfo                           .FieldType.GetGenericInterfaceTypeDefinitions().Contains(typeof(ISet<>));         }

Remember to add the collection type factory to your config..

configuration.<wbr />CollectionTypeFactory<<wbr />Net4CollectionTypeFactory>();

Lazy loading - eager loading

MarkCranness — Fri, 08 Jul 2011 22:54:56 GMT
Current revision posted to How to by MarkCranness on 08/07/2011 07:54:56 p.m.

Lazy loading - eager loading

Filed under: query, lazy loading

In this article I want to discuss the lazy loading mechanism provided by NHibernate. It is recommended for maximum flexibility to define all relations in your domain as lazy loadable. This is the default behavior of NHibernate since version 1.2. But this can lead to some undesired effects if querying your data. Let's discuss these effects and how to avoid them. Term Paper AND Research Paper

In my previous posts I showed how to prepare your system for NHibernate and how to implement a first NHibernate base application. This post is based on those two articles. Thesis AND Dissertation AND Essay

The Domain

Let's first define a simple domain. It shows part of an order entry system. I keep this model as simple as possible (a real domain model would be more complex) but it contains all aspects we want to discuss in this post. Below is the class diagram of our model

We have an order entity which can be placed by a customer entity. Each order can have many order line entities. Each of the three entity types is uniquely identified by a property Id (surrogate key).

The Mapping Files

We have to write one mapping file per entity. It is recommended that you always have one mapping per file. Don't forget to set the Build Action of each mapping file to Embedded Resource. People often tend to forget it and the subsequent errors raised by NHibernate are not always obvious. Also do not forget to give the mapping files the correct name, that is *.hbm.xml where * denotes the placeholder for the entity name.

The mapping for the Order entity might be implemented as follows

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="Order" table="Orders"> <id name="Id"> <generator class="guid"/> </id> <property name="OrderNumber"/> <property name="OrderDate"/> <many-to-one name="Customer" /> <set name="OrderLines" cascade="all-delete-orphan" > <key column="OrderId"/> <one-to-many class="OrderLine"/> </set> </class> </hibernate-mapping>

Analogous you can implement the mappings for the Customer entity

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="Customer"> <id name="Id"> <generator class="guid"/> </id> <property name="CompanyName"/> </class> </hibernate-mapping>

and finally the mapping for the OrderLine entity.

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="OrderLine"> <id name="Id"> <generator class="guid"/> </id> <property name="Amount"/> <property name="ProductName"/> </class> </hibernate-mapping>

Testing the Mapping

To test the mapping we use the following test method

using LazyLoadEagerLoad.Domain;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class GenerateSchema_Fixture

{

[Test]

public void Can_generate_schema()

{

var cfg = new Configuration();

cfg.Configure();

cfg.AddAssembly(typeof(Order).Assembly);

new SchemaExport(cfg).Execute(false, true, false, false);

}

}

}

First we create a new instance of the NHibernate Configuration class and tell it to configure itself. Since we don't provide any explicit configuration here in the code NHibernate looks out for an adequate configuration file. I have included such a file (called hibernate.cfg.xml) in my project. Please consult this previous post for further details about the configuration file.

Testing the Loading Behavior of NHibernate

Defining a base class for our tests

To avoid repetitive task (DRY principle) we implement the following base class.

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

public class TestFixtureBase

{

private Configuration _configuration;

private ISessionFactory _sessionFactory;

protected ISessionFactory SessionFactory

{

get { return _sessionFactory; }

}

[TestFixtureSetUp]

public void TestFixtureSetUp()

{

_configuration = new Configuration();

_configuration.Configure();

_configuration.AddAssembly(typeof(Customer).Assembly);

_sessionFactory = _configuration.BuildSessionFactory();

}

[TestFixtureTearDown]

public void TestFixtureTearDown()

{

_sessionFactory.Close();

}

[SetUp]

public void SetupContext()

{

new SchemaExport(_configuration).Execute(false, true, false, false);

Before_each_test();

}

[TearDown]

public void TearDownContext()

{

After_each_test();

}

protected virtual void Before_each_test()

{ }

protected virtual void After_each_test()

{ }

}

}

When the test fixture is started, the base class configures NHibernate and creates a session factory (TestFixtureSetUp). When the whole test fixture is ended the session factory is closed (TestFixtureTearDown).

Before each test in the fixture is run the database schema is (re-) created and the virtual Before_each_test method is called. After each test in the fixture is finished the virtual After_each_test method is called. The two virtual methods can (but must not necessarily) be overridden in a child class.

All our test fixtures we implement will derive from this base class.

Filling the database with test data

To be able to test the loading behavior of NHibernate we need some test data in our database. We create this test data every time a test is run (just after the database schema is re-created). We add a new class Order_Fixture to our test project and inherit from the TestFixtureBase base class. Then we override the Before_each_test method and call a helper method which creates our initial data. We create just the absolute minimum of data we need (again -->DRY). That is: one customer placing one order with two order lines.

using System;

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Criterion;

using NHibernate.SqlCommand;

using NUnit.Framework;

using Order=LazyLoadEagerLoad.Domain.Order;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class Order_Fixture : TestFixtureBase

{

private Order _order;

protected override void Before_each_test()

{

base.Before_each_test();

CreateInitialData();

}

private void CreateInitialData()

{

// create a single customer and an order with two order lines for this customer

var customer = new Customer {CompanyName = "IBM"};

var line1 = new OrderLine {Amount = 5, ProductName = "Laptop XYZ"};

var line2 = new OrderLine {Amount = 2, ProductName = "Desktop PC A100"};

_order = new Order

{

OrderNumber = "o-100-001",

OrderDate = DateTime.Today,

Customer = customer

};

_order.OrderLines.Add(line1);

_order.OrderLines.Add(line2);

using (ISession session = SessionFactory.OpenSession())

using (ITransaction transaction = session.BeginTransaction())

{

session.Save(customer);

session.Save(_order);

transaction.Commit();

}

}

}

}

The CreateInitialData method is run before each test. With this we guarantee that each test is side effects free.

Verifying the default behavior - Lazy Loading

When loading an order entity from database the default behavior of NHibernate is to lazy load all associated objects of the order entity. Let's write a test to verify this. For the verification we use a utility class provided by NHibernate (NHibernateUtil) which can test whether an associated object or object collection is initialized (i.e. loaded) or not. The class can also force the initialization of an un-initialized relation.

[Test] public void Customer_and_OrderLines_are_not_loaded_when_loading_Order() { Order fromDb; using (ISession session = SessionFactory.OpenSession()) fromDb = session.Get<Order>(_order.Id); Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer)); Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines)); }

The test succeeds and NHibernate generates SQL similar to this one

SELECT order0_.Id as Id0_0_, order0_.OrderNumber as OrderNum2_0_0_, order0_.OrderDate as OrderDate0_0_, order0_.CustomerId as CustomerId0_0_ FROM Orders order0_ WHERE order0_.Id='15bca5b3-2771-4bee-9923-85bda66318d8'

Now we have a problem: If we want to access the order line items (after the session has been closed) we get an exception. Since the session is closed NHibernate cannot lazily load the order line items for us. We can show this behavior with the following test method

[Test] [ExpectedException(typeof(LazyInitializationException))] public void Accessing_customer_of_order_after_session_is_closed_throws() { Order fromDb; using (ISession session = SessionFactory.OpenSession()) fromDb = session.Get<Order>(_order.Id); // trying to access the Customer of the order, will throw exception // Note: at this point the session is already closed string name = fromDb.Customer.CompanyName; }

Note: the above test only succeeds if the method throws the expected exception of type LazyInitializationException. And this is just what we want to show!

Another problem is the n+1 select statements problem. If we access the order line items after loading the order we generate a select statement for each line item we access. Thus if we have n line items and want to access them all we generate one select statement for the order itself and n select statements for all line items (result: n+1 select statements). This can make our data fetching rather slow and put a (unnecessary) burden onto our database.

We can simulate this behavior with this test method

[Test] public void Show_n_plus_1_select_behavior() { using (ISession session = SessionFactory.OpenSession()) { var fromDb = session.Get<Order>(_order.Id); int sum = 0; foreach (var line in fromDb.OrderLines) { // just some dummy code to force loading of order line sum += line.Amount; } } }

NHibernate will generate SQL similar to the following

SELECT order0_.Id as Id3_0_, order0_.OrderNumber as OrderNum2_3_0_, order0_.OrderDate as OrderDate3_0_, order0_.Customer as Customer3_0_ FROM Orders order0_ WHERE order0_.Id='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a' SELECT orderlines0_.OrderId as OrderId1_, orderlines0_.Id as Id1_, orderlines0_.Id as Id4_0_, orderlines0_.Amount as Amount4_0_, orderlines0_.ProductName as ProductN3_4_0_ FROM OrderLine orderlines0_ WHERE orderlines0_.OrderId='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a'

This time we have been lucky! NHibernate has automatically generated an optimized query for us and has loaded the 2 order line items in one go. But this is not always the case! Imagine having a collection with several 100 items and you only need to access one or two of them. It would be a waste of resources to always load all items.

But fortunately we have a solution for these kind of problems with NHibernate. It's called eagerly loading.

Eagerly loading with the NHibernateUtil class

If you know you need have access to related objects of the order entity you can use the NHibernateUtil class to initialize the related objects (that is: to fetch them from the database). Have a look at this test methods

[Test]

public void Can_initialize_customer_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.Customer);

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

[Test]

public void Can_initialize_order_lines_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.OrderLines);

}

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

With this utility class you can initialize single objects as well as collection of objects. In each case NHibernate will send 2 select statements to the database. One to select the order and one to initialize the related object(s).

Eagerly loading with HQL

If you know that you want to load all order items of a given order then you can tell NHibernate to do so and eagerly load all order lines together with the order in one go. The following test method shows how you can formulate a HQL query which not only loads the order but also the associated customer and order lines.

[Test]

public void Can_eagerly_load_order_aggregate_with_hql_query()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

string sql = "from Order o" +

" inner join fetch o.OrderLines" +

" inner join fetch o.Customer" +

" where o.Id=:id";

fromDb = session.CreateQuery(sql)

.SetGuid("id", _order.Id)

.UniqueResult<Order>();

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

The resulting sql generated by NHibernate is then similar to this one

select order0_.Id as Id0_0_, orderlines1_.Id as Id1_1_, customer2_.Id as Id2_2_, order0_.OrderNumber as OrderNum2_0_0_, order0_.OrderDate as OrderDate0_0_, order0_.CustomerId as CustomerId0_0_, orderlines1_.Amount as Amount1_1_, orderlines1_.ProductName as ProductN3_1_1_, customer2_.CompanyName as CompanyN2_2_2_, orderlines1_.OrderId as OrderId0__, orderlines1_.Id as Id0__ from Orders order0_ inner join OrderLine orderlines1_ on order0_.Id=orderlines1_.OrderId inner join Customer customer2_ on order0_.CustomerId=customer2_.Id where order0_.Id='409ebd99-3206-459b-bfed-6df989284da9'

NHibernate has created an SQL select statement which joins the 3 tables involved, namely Orders, Customer andOrderLine. The returned (flat) set of records is then used by NHibernate to build up the object tree with the order entity as a root.

Aggregates in the Domain

DDD defines the concept of aggregates. A short definition of an aggregate is "A cluster of associated objects that are treated as a unit for the purpose of data changes.". An aggregate always has a root. In this context we can define the following aggregate in our domain

The order entity is the root and the order lines belong to the aggregate (can be regarded as children of the root). When creating a new order or changing an existing one we only want to modify either the order itself or its order lines. We certainly do not want to change the customer entity because this would be a completely different use case and does not belong to the order management use case.

So, when dealing with aggregates we often want to load the complete aggregate in one go! This is the perfect example for using eager loading techniques.

Summary

I have introduced the concept of lazy loading as provided by NHibernate. I have discussed the consequences and shown how to avoid negative side effects by using different techniques of so called eager loading.

Lazy loading - eager loading

markweee — Wed, 30 Mar 2011 11:17:43 GMT
Revision 7 posted to How to by markweee on 30/03/2011 08:17:43 a.m.

Lazy loading - eager loading

Filed under: query, lazy loading

In this article I want to discuss the lazy loading mechanism provided by NHibernate. It is recommended for maximum flexibility to define all relations in your domain as lazy loadable. This is the default behavior of NHibernate since version 1.2. But this can lead to some undesired effects if querying your data. Let's discuss these effects and how to avoid them. Term Paper AND Research Paper

In my previous posts I showed how to prepare your system for NHibernate and how to implement a first NHibernate base application. This post is based on those two articles. Thesis AND Dissertation AND Essay

The Domain

Let's first define a simple domain. It shows part of an order entry system. I keep this model as simple as possible (a real domain model would be more complex) but it contains all aspects we want to discuss in this post. Below is the class diagram of our model

We have an order entity which can be placed by a customer entity. Each order can have many order line entities. Each of the three entity types is uniquely identified by a property Id (surrogate key).

The Mapping Files

We have to write one mapping file per entity. It is recommended that you always have one mapping per file. Don't forget to set the Build Action of each mapping file to Embedded Resource. People often tend to forget it and the subsequent errors raised by NHibernate are not always obvious. Also do not forget to give the mapping files the correct name, that is *.hbm.xml where * denotes the placeholder for the entity name.

The mapping for the Order entity might be implemented as follows

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="Order" table="Orders"> <id name="Id"> <generator class="guid"/> </id> <property name="OrderNumber"/> <property name="OrderDate"/> <many-to-one name="Customer" /> <set name="OrderLines" cascade="all-delete-orphan" > <key column="OrderId"/> <one-to-many class="OrderLine"/> </set> </class> </hibernate-mapping>

Analogous you can implement the mappings for the Customer entity

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="Customer"> <id name="Id"> <generator class="guid"/> </id> <property name="CompanyName"/> </class> </hibernate-mapping>

and finally the mapping for the OrderLine entity.

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="OrderLine"> <id name="Id"> <generator class="guid"/> </id> <property name="Amount"/> <property name="ProductName"/> </class> </hibernate-mapping>

Testing the Mapping

To test the mapping we use the following test method

using LazyLoadEagerLoad.Domain;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class GenerateSchema_Fixture

{

[Test]

public void Can_generate_schema()

{

var cfg = new Configuration();

cfg.Configure();

cfg.AddAssembly(typeof(Order).Assembly);

new SchemaExport(cfg).Execute(false, true, false, false);

}

}

}

First we create a new instance of the NHibernate Configuration class and tell it to configure itself. Since we don't provide any explicit configuration here in the code NHibernate looks out for an adequate configuration file. I have included such a file (called hibernate.cfg.xml) in my project. Please consult this previous post for further details about the configuration file.

Testing the Loading Behavior of NHibernate

Defining a base class for our tests

To avoid repetitive task (DRY principle) we implement the following base class.

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

public class TestFixtureBase

{

private Configuration _configuration;

private ISessionFactory _sessionFactory;

protected ISessionFactory SessionFactory

{

get { return _sessionFactory; }

}

[TestFixtureSetUp]

public void TestFixtureSetUp()

{

_configuration = new Configuration();

_configuration.Configure();

_configuration.AddAssembly(typeof(Customer).Assembly);

_sessionFactory = _configuration.BuildSessionFactory();

}

[TestFixtureTearDown]

public void TestFixtureTearDown()

{

_sessionFactory.Close();

}

[SetUp]

public void SetupContext()

{

new SchemaExport(_configuration).Execute(false, true, false, false);

Before_each_test();

}

[TearDown]

public void TearDownContext()

{

After_each_test();

}

protected virtual void Before_each_test()

{ }

protected virtual void After_each_test()

{ }

}

}

When the test fixture is started, the base class configures NHibernate and creates a session factory (TestFixtureSetUp). When the whole test fixture is ended the session factory is closed (TestFixtureTearDown).

Before each test in the fixture is run the database schema is (re-) created and the virtual Before_each_test method is called. After each test in the fixture is finished the virtual After_each_test method is called. The two virtual methods can (but must not necessarily) be overridden in a child class.

All our test fixtures we implement will derive from this base class.

Filling the database with test data

To be able to test the loading behavior of NHibernate we need some test data in our database. We create this test data every time a test is run (just after the database schema is re-created). We add a new class Order_Fixture to our test project and inherit from the TestFixtureBase base class. Then we override the Before_each_test method and call a helper method which creates our initial data. We create just the absolute minimum of data we need (again -->DRY). That is: one customer placing one order with two order lines.

using System;

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Criterion;

using NHibernate.SqlCommand;

using NUnit.Framework;

using Order=LazyLoadEagerLoad.Domain.Order;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class Order_Fixture : TestFixtureBase

{

private Order _order;

protected override void Before_each_test()

{

base.Before_each_test();

CreateInitialData();

}

private void CreateInitialData()

{

// create a single customer and an order with two order lines for this customer

var customer = new Customer {CompanyName = "IBM"};

var line1 = new OrderLine {Amount = 5, ProductName = "Laptop XYZ"};

var line2 = new OrderLine {Amount = 2, ProductName = "Desktop PC A100"};

_order = new Order

{

OrderNumber = "o-100-001",

OrderDate = DateTime.Today,

Customer = customer

};

_order.OrderLines.Add(line1);

_order.OrderLines.Add(line2);

using (ISession session = SessionFactory.OpenSession())

using (ITransaction transaction = session.BeginTransaction())

{

session.Save(customer);

session.Save(_order);

transaction.Commit();

}

}

}

}

The CreateInitialData method is run before each test. With this we guarantee that each test is side effects free.

Verifying the default behavior - Lazy Loading

When loading an order entity from database the default behavior of NHibernate is to lazy load all associated objects of the order entity. Let's write a test to verify this. For the verification we use a utility class provided by NHibernate (NHibernateUtil) which can test whether an associated object or object collection is initialized (i.e. loaded) or not. The class can also force the initialization of an un-initialized relation.

[Test] public void Customer_and_OrderLines_are_not_loaded_when_loading_Order() { Order fromDb; using (ISession session = SessionFactory.OpenSession()) fromDb = session.Get<Order>(_order.Id); Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer)); Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines)); }

The test succeeds and NHibernate generates SQL similar to this one

SELECT order0_.Id as Id0_0_, order0_.OrderNumber as OrderNum2_0_0_, order0_.OrderDate as OrderDate0_0_, order0_.CustomerId as CustomerId0_0_ FROM Orders order0_ WHERE order0_.Id='15bca5b3-2771-4bee-9923-85bda66318d8'

Now we have a problem: If we want to access the order line items (after the session has been closed) we get an exception. Since the session is closed NHibernate cannot lazily load the order line items for us. We can show this behavior with the following test method

[Test] [ExpectedException(typeof(LazyInitializationException))] public void Accessing_customer_of_order_after_session_is_closed_throws() { Order fromDb; using (ISession session = SessionFactory.OpenSession()) fromDb = session.Get<Order>(_order.Id); // trying to access the Customer of the order, will throw exception // Note: at this point the session is already closed string name = fromDb.Customer.CompanyName; }

Note: the above test only succeeds if the method throws the expected exception of type LazyInitializationException. And this is just what we want to show!

Another problem is the n+1 select statements problem. If we access the order line items after loading the order we generate a select statement for each line item we access. Thus if we have n line items and want to access them all we generate one select statement for the order itself and n select statements for all line items (result: n+1 select statements). This can make our data fetching rather slow and put a (unnecessary) burden onto our database.

We can simulate this behavior with this test method

[Test] public void Show_n_plus_1_select_behavior() { using (ISession session = SessionFactory.OpenSession()) { var fromDb = session.Get<Order>(_order.Id); int sum = 0; foreach (var line in fromDb.OrderLines) { // just some dummy code to force loading of order line sum += line.Amount; } } }

NHibernate will generate SQL similar to the following

SELECT order0_.Id as Id3_0_, order0_.OrderNumber as OrderNum2_3_0_, order0_.OrderDate as OrderDate3_0_, order0_.Customer as Customer3_0_ FROM Orders order0_ WHERE order0_.Id='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a' SELECT orderlines0_.OrderId as OrderId1_, orderlines0_.Id as Id1_, orderlines0_.Id as Id4_0_, orderlines0_.Amount as Amount4_0_, orderlines0_.ProductName as ProductN3_4_0_ FROM OrderLine orderlines0_ WHERE orderlines0_.OrderId='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a'

This time we have been lucky! NHibernate has automatically generated an optimized query for us and has loaded the 2 order line items in one go. But this is not always the case! Imagine having a collection with several 100 items and you only need to access one or two of them. It would be a waste of resources to always load all items.

But fortunately we have a solution for these kind of problems with NHibernate. It's called eagerly loading.

Eagerly loading with the NHibernateUtil class

If you know you need have access to related objects of the order entity you can use the NHibernateUtil class to initialize the related objects (that is: to fetch them from the database). Have a look at this test methods

[Test]

public void Can_initialize_customer_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.Customer);

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

[Test]

public void Can_initialize_order_lines_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.OrderLines);

}

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

With this utility class you can initialize single objects as well as collection of objects. In each case NHibernate will send 2 select statements to the database. One to select the order and one to initialize the related object(s).

Eagerly loading with HQL

If you know that you want to load all order items of a given order then you can tell NHibernate to do so and eagerly load all order lines together with the order in one go. The following test method shows how you can formulate a HQL query which not only loads the order but also the associated customer and order lines.

[Test]

public void Can_eagerly_load_order_aggregate_with_hql_query()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

string sql = "from Order o" +

" inner join fetch o.OrderLines" +

" inner join fetch o.Customer" +

" where o.Id=:id";

fromDb = session.CreateQuery(sql)

.SetGuid("id", _order.Id)

.UniqueResult<Order>();

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

The resulting sql generated by NHibernate is then similar to this one

select order0_.Id as Id0_0_, orderlines1_.Id as Id1_1_, customer2_.Id as Id2_2_, order0_.OrderNumber as OrderNum2_0_0_, order0_.OrderDate as OrderDate0_0_, order0_.CustomerId as CustomerId0_0_, orderlines1_.Amount as Amount1_1_, orderlines1_.ProductName as ProductN3_1_1_, customer2_.CompanyName as CompanyN2_2_2_, orderlines1_.OrderId as OrderId0__, orderlines1_.Id as Id0__ from Orders order0_ inner join OrderLine orderlines1_ on order0_.Id=orderlines1_.OrderId inner join Customer customer2_ on order0_.CustomerId=customer2_.Id where order0_.Id='409ebd99-3206-459b-bfed-6df989284da9'

NHibernate has created an SQL select statement which joins the 3 tables involved, namely Orders, Customer andOrderLine. The returned (flat) set of records is then used by NHibernate to build up the object tree with the order entity as a root.

Aggregates in the Domain

DDD defines the concept of aggregates. A short definition of an aggregate is "A cluster of associated objects that are treated as a unit for the purpose of data changes.". An aggregate always has a root. In this context we can define the following aggregate in our domain

The order entity is the root and the order lines belong to the aggregate (can be regarded as children of the root). When creating a new order or changing an existing one we only want to modify either the order itself or its order lines. We certainly do not want to change the customer entity because this would be a completely different use case and does not belong to the order management use case.

So, when dealing with aggregates we often want to load the complete aggregate in one go! This is the perfect example for using eager loading techniques.

Summary

I have introduced the concept of lazy loading as provided by NHibernate. I have discussed the consequences and shown how to avoid negative side effects by using different techniques of so called eager loading.

Lazy loading - eager loading

Fabio Maulo — Wed, 10 Sep 2008 14:32:59 GMT
Revision 6 posted to How to by Fabio Maulo on 10/09/2008 11:32:59 a.m.

Lazy loading - eager loading

Filed under: query, lazy loading

In this article I want to discuss the lazy loading mechanism provided by NHibernate. It is recommended for maximum flexibility to define all relations in your domain as lazy loadable. This is the default behavior of NHibernate since version 1.2. But this can lead to some undesired effects if querying your data. Let's discuss these effects and how to avoid them.

In my previous posts I showed how to prepare your system for NHibernate and how to implement a first NHibernate base application. This post is based on those two articles.

The Domain

Let's first define a simple domain. It shows part of an order entry system. I keep this model as simple as possible (a real domain model would be more complex) but it contains all aspects we want to discuss in this post. Below is the class diagram of our model

We have an order entity which can be placed by a customer entity. Each order can have many order line entities. Each of the three entity types is uniquely identified by a property Id (surrogate key).

The Mapping Files

We have to write one mapping file per entity. It is recommended that you always have one mapping per file. Don't forget to set the Build Action of each mapping file to Embedded Resource. People often tend to forget it and the subsequent errors raised by NHibernate are not always obvious. Also do not forget to give the mapping files the correct name, that is *.hbm.xml where * denotes the placeholder for the entity name.

The mapping for the Order entity might be implemented as follows

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="Order" table="Orders"> <id name="Id"> <generator class="guid"/> </id> <property name="OrderNumber"/> <property name="OrderDate"/> <many-to-one name="Customer" /> <set name="OrderLines" cascade="all-delete-orphan" > <key column="OrderId"/> <one-to-many class="OrderLine"/> </set> </class> </hibernate-mapping>

Analogous you can implement the mappings for the Customer entity

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="Customer"> <id name="Id"> <generator class="guid"/> </id> <property name="CompanyName"/> </class> </hibernate-mapping>

and finally the mapping for the OrderLine entity.

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="OrderLine"> <id name="Id"> <generator class="guid"/> </id> <property name="Amount"/> <property name="ProductName"/> </class> </hibernate-mapping>

Testing the Mapping

To test the mapping we use the following test method

using LazyLoadEagerLoad.Domain;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class GenerateSchema_Fixture

{

[Test]

public void Can_generate_schema()

{

var cfg = new Configuration();

cfg.Configure();

cfg.AddAssembly(typeof(Order).Assembly);

new SchemaExport(cfg).Execute(false, true, false, false);

}

}

}

First we create a new instance of the NHibernate Configuration class and tell it to configure itself. Since we don't provide any explicit configuration here in the code NHibernate looks out for an adequate configuration file. I have included such a file (called hibernate.cfg.xml) in my project. Please consult this previous post for further details about the configuration file.

Testing the Loading Behavior of NHibernate

Defining a base class for our tests

To avoid repetitive task (DRY principle) we implement the following base class.

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

public class TestFixtureBase

{

private Configuration _configuration;

private ISessionFactory _sessionFactory;

protected ISessionFactory SessionFactory

{

get { return _sessionFactory; }

}

[TestFixtureSetUp]

public void TestFixtureSetUp()

{

_configuration = new Configuration();

_configuration.Configure();

_configuration.AddAssembly(typeof(Customer).Assembly);

_sessionFactory = _configuration.BuildSessionFactory();

}

[TestFixtureTearDown]

public void TestFixtureTearDown()

{

_sessionFactory.Close();

}

[SetUp]

public void SetupContext()

{

new SchemaExport(_configuration).Execute(false, true, false, false);

Before_each_test();

}

[TearDown]

public void TearDownContext()

{

After_each_test();

}

protected virtual void Before_each_test()

{ }

protected virtual void After_each_test()

{ }

}

}

When the test fixture is started, the base class configures NHibernate and creates a session factory (TestFixtureSetUp). When the whole test fixture is ended the session factory is closed (TestFixtureTearDown).

Before each test in the fixture is run the database schema is (re-) created and the virtual Before_each_test method is called. After each test in the fixture is finished the virtual After_each_test method is called. The two virtual methods can (but must not necessarily) be overridden in a child class.

All our test fixtures we implement will derive from this base class.

Filling the database with test data

To be able to test the loading behavior of NHibernate we need some test data in our database. We create this test data every time a test is run (just after the database schema is re-created). We add a new class Order_Fixture to our test project and inherit from the TestFixtureBase base class. Then we override the Before_each_test method and call a helper method which creates our initial data. We create just the absolute minimum of data we need (again -->DRY). That is: one customer placing one order with two order lines.

using System;

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Criterion;

using NHibernate.SqlCommand;

using NUnit.Framework;

using Order=LazyLoadEagerLoad.Domain.Order;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class Order_Fixture : TestFixtureBase

{

private Order _order;

protected override void Before_each_test()

{

base.Before_each_test();

CreateInitialData();

}

private void CreateInitialData()

{

// create a single customer and an order with two order lines for this customer

var customer = new Customer {CompanyName = "IBM"};

var line1 = new OrderLine {Amount = 5, ProductName = "Laptop XYZ"};

var line2 = new OrderLine {Amount = 2, ProductName = "Desktop PC A100"};

_order = new Order

{

OrderNumber = "o-100-001",

OrderDate = DateTime.Today,

Customer = customer

};

_order.OrderLines.Add(line1);

_order.OrderLines.Add(line2);

using (ISession session = SessionFactory.OpenSession())

using (ITransaction transaction = session.BeginTransaction())

{

session.Save(customer);

session.Save(_order);

transaction.Commit();

}

}

}

}

The CreateInitialData method is run before each test. With this we guarantee that each test is side effects free.

Verifying the default behavior - Lazy Loading

When loading an order entity from database the default behavior of NHibernate is to lazy load all associated objects of the order entity. Let's write a test to verify this. For the verification we use a utility class provided by NHibernate (NHibernateUtil) which can test whether an associated object or object collection is initialized (i.e. loaded) or not. The class can also force the initialization of an un-initialized relation.

[Test] public void Customer_and_OrderLines_are_not_loaded_when_loading_Order() { Order fromDb; using (ISession session = SessionFactory.OpenSession()) fromDb = session.Get<Order>(_order.Id); Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer)); Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines)); }

The test succeeds and NHibernate generates SQL similar to this one

SELECT order0_.Id as Id0_0_, order0_.OrderNumber as OrderNum2_0_0_, order0_.OrderDate as OrderDate0_0_, order0_.CustomerId as CustomerId0_0_ FROM Orders order0_ WHERE order0_.Id='15bca5b3-2771-4bee-9923-85bda66318d8'

Now we have a problem: If we want to access the order line items (after the session has been closed) we get an exception. Since the session is closed NHibernate cannot lazily load the order line items for us. We can show this behavior with the following test method

[Test] [ExpectedException(typeof(LazyInitializationException))] public void Accessing_customer_of_order_after_session_is_closed_throws() { Order fromDb; using (ISession session = SessionFactory.OpenSession()) fromDb = session.Get<Order>(_order.Id); // trying to access the Customer of the order, will throw exception // Note: at this point the session is already closed string name = fromDb.Customer.CompanyName; }

Note: the above test only succeeds if the method throws the expected exception of type LazyInitializationException. And this is just what we want to show!

Another problem is the n+1 select statements problem. If we access the order line items after loading the order we generate a select statement for each line item we access. Thus if we have n line items and want to access them all we generate one select statement for the order itself and n select statements for all line items (result: n+1 select statements). This can make our data fetching rather slow and put a (unnecessary) burden onto our database.

We can simulate this behavior with this test method

[Test] public void Show_n_plus_1_select_behavior() { using (ISession session = SessionFactory.OpenSession()) { var fromDb = session.Get<Order>(_order.Id); int sum = 0; foreach (var line in fromDb.OrderLines) { // just some dummy code to force loading of order line sum += line.Amount; } } }

NHibernate will generate SQL similar to the following

SELECT order0_.Id as Id3_0_, order0_.OrderNumber as OrderNum2_3_0_, order0_.OrderDate as OrderDate3_0_, order0_.Customer as Customer3_0_ FROM Orders order0_ WHERE order0_.Id='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a' SELECT orderlines0_.OrderId as OrderId1_, orderlines0_.Id as Id1_, orderlines0_.Id as Id4_0_, orderlines0_.Amount as Amount4_0_, orderlines0_.ProductName as ProductN3_4_0_ FROM OrderLine orderlines0_ WHERE orderlines0_.OrderId='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a'

This time we have been lucky! NHibernate has automatically generated an optimized query for us and has loaded the 2 order line items in one go. But this is not always the case! Imagine having a collection with several 100 items and you only need to access one or two of them. It would be a waste of resources to always load all items.

But fortunately we have a solution for these kind of problems with NHibernate. It's called eagerly loading.

Eagerly loading with the NHibernateUtil class

If you know you need have access to related objects of the order entity you can use the NHibernateUtil class to initialize the related objects (that is: to fetch them from the database). Have a look at this test methods

[Test]

public void Can_initialize_customer_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.Customer);

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

[Test]

public void Can_initialize_order_lines_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.OrderLines);

}

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

With this utility class you can initialize single objects as well as collection of objects. In each case NHibernate will send 2 select statements to the database. One to select the order and one to initialize the related object(s).

Eagerly loading with HQL

If you know that you want to load all order items of a given order then you can tell NHibernate to do so and eagerly load all order lines together with the order in one go. The following test method shows how you can formulate a HQL query which not only loads the order but also the associated customer and order lines.

[Test]

public void Can_eagerly_load_order_aggregate_with_hql_query()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

string sql = "from Order o" +

" inner join fetch o.OrderLines" +

" inner join fetch o.Customer" +

" where o.Id=:id";

fromDb = session.CreateQuery(sql)

.SetGuid("id", _order.Id)

.UniqueResult<Order>();

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

The resulting sql generated by NHibernate is then similar to this one

select order0_.Id as Id0_0_, orderlines1_.Id as Id1_1_, customer2_.Id as Id2_2_, order0_.OrderNumber as OrderNum2_0_0_, order0_.OrderDate as OrderDate0_0_, order0_.CustomerId as CustomerId0_0_, orderlines1_.Amount as Amount1_1_, orderlines1_.ProductName as ProductN3_1_1_, customer2_.CompanyName as CompanyN2_2_2_, orderlines1_.OrderId as OrderId0__, orderlines1_.Id as Id0__ from Orders order0_ inner join OrderLine orderlines1_ on order0_.Id=orderlines1_.OrderId inner join Customer customer2_ on order0_.CustomerId=customer2_.Id where order0_.Id='409ebd99-3206-459b-bfed-6df989284da9'

NHibernate has created an SQL select statement which joins the 3 tables involved, namely Orders, Customer andOrderLine. The returned (flat) set of records is then used by NHibernate to build up the object tree with the order entity as a root.

Aggregates in the Domain

DDD defines the concept of aggregates. A short definition of an aggregate is "A cluster of associated objects that are treated as a unit for the purpose of data changes.". An aggregate always has a root. In this context we can define the following aggregate in our domain

The order entity is the root and the order lines belong to the aggregate (can be regarded as children of the root). When creating a new order or changing an existing one we only want to modify either the order itself or its order lines. We certainly do not want to change the customer entity because this would be a completely different use case and does not belong to the order management use case.

So, when dealing with aggregates we often want to load the complete aggregate in one go! This is the perfect example for using eager loading techniques.

Summary

I have introduced the concept of lazy loading as provided by NHibernate. I have discussed the consequences and shown how to avoid negative side effects by using different techniques of so called eager loading.

Lazy loading - eager loading

Fabio Maulo — Sun, 07 Sep 2008 04:34:42 GMT
Revision 5 posted to How to by Fabio Maulo on 07/09/2008 01:34:42 a.m.

Lazy loading - eager loading

In this article I want to discuss the lazy loading mechanism provided by NHibernate. It is recommended for maximum flexibility to define all relations in your domain as lazy loadable. This is the default behavior of NHibernate since version 1.2. But this can lead to some undesired effects if querying your data. Let's discuss these effects and how to avoid them.

In my previous posts I showed how to prepare your system for NHibernate and how to implement a first NHibernate base application. This post is based on those two articles.

The Domain

Let's first define a simple domain. It shows part of an order entry system. I keep this model as simple as possible (a real domain model would be more complex) but it contains all aspects we want to discuss in this post. Below is the class diagram of our model

We have an order entity which can be placed by a customer entity. Each order can have many order line entities. Each of the three entity types is uniquely identified by a property Id (surrogate key).

The Mapping Files

We have to write one mapping file per entity. It is recommended that you always have one mapping per file. Don't forget to set the Build Action of each mapping file to Embedded Resource. People often tend to forget it and the subsequent errors raised by NHibernate are not always obvious. Also do not forget to give the mapping files the correct name, that is *.hbm.xml where * denotes the placeholder for the entity name.

The mapping for the Order entity might be implemented as follows

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="Order" table="Orders"> <id name="Id"> <generator class="guid"/> </id> <property name="OrderNumber"/> <property name="OrderDate"/> <many-to-one name="Customer" /> <set name="OrderLines" cascade="all-delete-orphan" > <key column="OrderId"/> <one-to-many class="OrderLine"/> </set> </class> </hibernate-mapping>

Analogous you can implement the mappings for the Customer entity

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="Customer"> <id name="Id"> <generator class="guid"/> </id> <property name="CompanyName"/> </class> </hibernate-mapping>

and finally the mapping for the OrderLine entity.

<?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="OrderLine"> <id name="Id"> <generator class="guid"/> </id> <property name="Amount"/> <property name="ProductName"/> </class> </hibernate-mapping>

Testing the Mapping

To test the mapping we use the following test method

using LazyLoadEagerLoad.Domain;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class GenerateSchema_Fixture

{

[Test]

public void Can_generate_schema()

{

var cfg = new Configuration();

cfg.Configure();

cfg.AddAssembly(typeof(Order).Assembly);

new SchemaExport(cfg).Execute(false, true, false, false);

}

}

}

First we create a new instance of the NHibernate Configuration class and tell it to configure itself. Since we don't provide any explicit configuration here in the code NHibernate looks out for an adequate configuration file. I have included such a file (called hibernate.cfg.xml) in my project. Please consult this previous post for further details about the configuration file.

Testing the Loading Behavior of NHibernate

Defining a base class for our tests

To avoid repetitive task (DRY principle) we implement the following base class.

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

public class TestFixtureBase

{

private Configuration _configuration;

private ISessionFactory _sessionFactory;

protected ISessionFactory SessionFactory

{

get { return _sessionFactory; }

}

[TestFixtureSetUp]

public void TestFixtureSetUp()

{

_configuration = new Configuration();

_configuration.Configure();

_configuration.AddAssembly(typeof(Customer).Assembly);

_sessionFactory = _configuration.BuildSessionFactory();

}

[TestFixtureTearDown]

public void TestFixtureTearDown()

{

_sessionFactory.Close();

}

[SetUp]

public void SetupContext()

{

new SchemaExport(_configuration).Execute(false, true, false, false);

Before_each_test();

}

[TearDown]

public void TearDownContext()

{

After_each_test();

}

protected virtual void Before_each_test()

{ }

protected virtual void After_each_test()

{ }

}

}

When the test fixture is started, the base class configures NHibernate and creates a session factory (TestFixtureSetUp). When the whole test fixture is ended the session factory is closed (TestFixtureTearDown).

Before each test in the fixture is run the database schema is (re-) created and the virtual Before_each_test method is called. After each test in the fixture is finished the virtual After_each_test method is called. The two virtual methods can (but must not necessarily) be overridden in a child class.

All our test fixtures we implement will derive from this base class.

Filling the database with test data

To be able to test the loading behavior of NHibernate we need some test data in our database. We create this test data every time a test is run (just after the database schema is re-created). We add a new class Order_Fixture to our test project and inherit from the TestFixtureBase base class. Then we override the Before_each_test method and call a helper method which creates our initial data. We create just the absolute minimum of data we need (again -->DRY). That is: one customer placing one order with two order lines.

using System;

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Criterion;

using NHibernate.SqlCommand;

using NUnit.Framework;

using Order=LazyLoadEagerLoad.Domain.Order;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class Order_Fixture : TestFixtureBase

{

private Order _order;

protected override void Before_each_test()

{

base.Before_each_test();

CreateInitialData();

}

private void CreateInitialData()

{

// create a single customer and an order with two order lines for this customer

var customer = new Customer {CompanyName = "IBM"};

var line1 = new OrderLine {Amount = 5, ProductName = "Laptop XYZ"};

var line2 = new OrderLine {Amount = 2, ProductName = "Desktop PC A100"};

_order = new Order

{

OrderNumber = "o-100-001",

OrderDate = DateTime.Today,

Customer = customer

};

_order.OrderLines.Add(line1);

_order.OrderLines.Add(line2);

using (ISession session = SessionFactory.OpenSession())

using (ITransaction transaction = session.BeginTransaction())

{

session.Save(customer);

session.Save(_order);

transaction.Commit();

}

}

}

}

The CreateInitialData method is run before each test. With this we guarantee that each test is side effects free.

Verifying the default behavior - Lazy Loading

When loading an order entity from database the default behavior of NHibernate is to lazy load all associated objects of the order entity. Let's write a test to verify this. For the verification we use a utility class provided by NHibernate (NHibernateUtil) which can test whether an associated object or object collection is initialized (i.e. loaded) or not. The class can also force the initialization of an un-initialized relation.

[Test] public void Customer_and_OrderLines_are_not_loaded_when_loading_Order() { Order fromDb; using (ISession session = SessionFactory.OpenSession()) fromDb = session.Get<Order>(_order.Id); Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer)); Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines)); }

The test succeeds and NHibernate generates SQL similar to this one

SELECT order0_.Id as Id0_0_, order0_.OrderNumber as OrderNum2_0_0_, order0_.OrderDate as OrderDate0_0_, order0_.CustomerId as CustomerId0_0_ FROM Orders order0_ WHERE order0_.Id='15bca5b3-2771-4bee-9923-85bda66318d8'

Now we have a problem: If we want to access the order line items (after the session has been closed) we get an exception. Since the session is closed NHibernate cannot lazily load the order line items for us. We can show this behavior with the following test method

[Test] [ExpectedException(typeof(LazyInitializationException))] public void Accessing_customer_of_order_after_session_is_closed_throws() { Order fromDb; using (ISession session = SessionFactory.OpenSession()) fromDb = session.Get<Order>(_order.Id); // trying to access the Customer of the order, will throw exception // Note: at this point the session is already closed string name = fromDb.Customer.CompanyName; }

Note: the above test only succeeds if the method throws the expected exception of type LazyInitializationException. And this is just what we want to show!

Another problem is the n+1 select statements problem. If we access the order line items after loading the order we generate a select statement for each line item we access. Thus if we have n line items and want to access them all we generate one select statement for the order itself and n select statements for all line items (result: n+1 select statements). This can make our data fetching rather slow and put a (unnecessary) burden onto our database.

We can simulate this behavior with this test method

[Test] public void Show_n_plus_1_select_behavior() { using (ISession session = SessionFactory.OpenSession()) { var fromDb = session.Get<Order>(_order.Id); int sum = 0; foreach (var line in fromDb.OrderLines) { // just some dummy code to force loading of order line sum += line.Amount; } } }

NHibernate will generate SQL similar to the following

SELECT order0_.Id as Id3_0_, order0_.OrderNumber as OrderNum2_3_0_, order0_.OrderDate as OrderDate3_0_, order0_.Customer as Customer3_0_ FROM Orders order0_ WHERE order0_.Id='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a' SELECT orderlines0_.OrderId as OrderId1_, orderlines0_.Id as Id1_, orderlines0_.Id as Id4_0_, orderlines0_.Amount as Amount4_0_, orderlines0_.ProductName as ProductN3_4_0_ FROM OrderLine orderlines0_ WHERE orderlines0_.OrderId='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a'

This time we have been lucky! NHibernate has automatically generated an optimized query for us and has loaded the 2 order line items in one go. But this is not always the case! Imagine having a collection with several 100 items and you only need to access one or two of them. It would be a waste of resources to always load all items.

But fortunately we have a solution for these kind of problems with NHibernate. It's called eagerly loading.

Eagerly loading with the NHibernateUtil class

If you know you need have access to related objects of the order entity you can use the NHibernateUtil class to initialize the related objects (that is: to fetch them from the database). Have a look at this test methods

[Test]

public void Can_initialize_customer_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.Customer);

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

[Test]

public void Can_initialize_order_lines_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.OrderLines);

}

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

With this utility class you can initialize single objects as well as collection of objects. In each case NHibernate will send 2 select statements to the database. One to select the order and one to initialize the related object(s).

Eagerly loading with HQL

If you know that you want to load all order items of a given order then you can tell NHibernate to do so and eagerly load all order lines together with the order in one go. The following test method shows how you can formulate a HQL query which not only loads the order but also the associated customer and order lines.

[Test]

public void Can_eagerly_load_order_aggregate_with_hql_query()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

string sql = "from Order o" +

" inner join fetch o.OrderLines" +

" inner join fetch o.Customer" +

" where o.Id=:id";

fromDb = session.CreateQuery(sql)

.SetGuid("id", _order.Id)

.UniqueResult<Order>();

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

The resulting sql generated by NHibernate is then similar to this one

select order0_.Id as Id0_0_, orderlines1_.Id as Id1_1_, customer2_.Id as Id2_2_, order0_.OrderNumber as OrderNum2_0_0_, order0_.OrderDate as OrderDate0_0_, order0_.CustomerId as CustomerId0_0_, orderlines1_.Amount as Amount1_1_, orderlines1_.ProductName as ProductN3_1_1_, customer2_.CompanyName as CompanyN2_2_2_, orderlines1_.OrderId as OrderId0__, orderlines1_.Id as Id0__ from Orders order0_ inner join OrderLine orderlines1_ on order0_.Id=orderlines1_.OrderId inner join Customer customer2_ on order0_.CustomerId=customer2_.Id where order0_.Id='409ebd99-3206-459b-bfed-6df989284da9'

NHibernate has created an SQL select statement which joins the 3 tables involved, namely Orders, Customer andOrderLine. The returned (flat) set of records is then used by NHibernate to build up the object tree with the order entity as a root.

Aggregates in the Domain

DDD defines the concept of aggregates. A short definition of an aggregate is "A cluster of associated objects that are treated as a unit for the purpose of data changes.". An aggregate always has a root. In this context we can define the following aggregate in our domain

The order entity is the root and the order lines belong to the aggregate (can be regarded as children of the root). When creating a new order or changing an existing one we only want to modify either the order itself or its order lines. We certainly do not want to change the customer entity because this would be a completely different use case and does not belong to the order management use case.

So, when dealing with aggregates we often want to load the complete aggregate in one go! This is the perfect example for using eager loading techniques.

Summary

I have introduced the concept of lazy loading as provided by NHibernate. I have discussed the consequences and shown how to avoid negative side effects by using different techniques of so called eager loading.

Lazy loading - eager loading

Fabio Maulo — Sun, 07 Sep 2008 04:33:15 GMT
Revision 4 posted to How to by Fabio Maulo on 07/09/2008 01:33:15 a.m.

Lazy loading - eager loading

In this article I want to discuss the lazy loading mechanism provided by NHibernate. It is recommended for maximum flexibility to define all relations in your domain as lazy loadable. This is the default behavior of NHibernate since version 1.2. But this can lead to some undesired effects if querying your data. Let's discuss these effects and how to avoid them.

In my previous posts I showed how to prepare your system for NHibernate and how to implement a first NHibernate base application. This post is based on those two articles.

The Domain

Let's first define a simple domain. It shows part of an order entry system. I keep this model as simple as possible (a real domain model would be more complex) but it contains all aspects we want to discuss in this post. Below is the class diagram of our model

We have an order entity which can be placed by a customer entity. Each order can have many order line entities. Each of the three entity types is uniquely identified by a property Id (surrogate key).

The Mapping Files

We have to write one mapping file per entity. It is recommended that you always have one mapping per file. Don't forget to set the Build Action of each mapping file to Embedded Resource. People often tend to forget it and the subsequent errors raised by NHibernate are not always obvious. Also do not forget to give the mapping files the correct name, that is *.hbm.xml where * denotes the placeholder for the entity name.

The mapping for the Order entity might be implemented as follows

<?xml version=version="1.0" encoding=encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="Order" table="Orders"> <id name="Id"> <generator class="guid"/> </id> <property name="OrderNumber"/> <property name="OrderDate"/> <many-to-one name="Customer" /> <set name="OrderLines" cascade="all-delete-orphan" > <key column="OrderId"/> <one-to-many class="OrderLine"/> </set> </class> </hibernate-mapping>

Analogous you can implement the mappings for the Customer entity

<?xml version=version="1.0" encoding=encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="Customer"> <id name="Id"> <generator class="guid"/> </id> <property name="CompanyName"/> </class> </hibernate-mapping>

and finally the mapping for the OrderLine entity.

<?xml version=version="1.0" encoding=encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="LazyLoadEagerLoad" namespace="LazyLoadEagerLoad.Domain"> <class name="OrderLine"> <id name="Id"> <generator class="guid"/> </id> <property name="Amount"/> <property name="ProductName"/> </class> </hibernate-mapping>

Testing the Mapping

To test the mapping we use the following test method

using LazyLoadEagerLoad.Domain;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class GenerateSchema_Fixture

{

[Test]

public void Can_generate_schema()

{

var cfg = new Configuration();

cfg.Configure();

cfg.AddAssembly(typeof(Order).Assembly);

new SchemaExport(cfg).Execute(false, true, false, false);

}

}

}

First we create a new instance of the NHibernate Configuration class and tell it to configure itself. Since we don't provide any explicit configuration here in the code NHibernate looks out for an adequate configuration file. I have included such a file (called hibernate.cfg.xml) in my project. Please consult this previous post for further details about the configuration file.

Testing the Loading Behavior of NHibernate

Defining a base class for our tests

To avoid repetitive task (DRY principle) we implement the following base class.

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

public class TestFixtureBase

{

private Configuration _configuration;

private ISessionFactory _sessionFactory;

protected ISessionFactory SessionFactory

{

get { return _sessionFactory; }

}

[TestFixtureSetUp]

public void TestFixtureSetUp()

{

_configuration = new Configuration();

_configuration.Configure();

_configuration.AddAssembly(typeof(Customer).Assembly);

_sessionFactory = _configuration.BuildSessionFactory();

}

[TestFixtureTearDown]

public void TestFixtureTearDown()

{

_sessionFactory.Close();

}

[SetUp]

public void SetupContext()

{

new SchemaExport(_configuration).Execute(false, true, false, false);

Before_each_test();

}

[TearDown]

public void TearDownContext()

{

After_each_test();

}

protected virtual void Before_each_test()

{ }

protected virtual void After_each_test()

{ }

}

}

When the test fixture is started, the base class configures NHibernate and creates a session factory (TestFixtureSetUp). When the whole test fixture is ended the session factory is closed (TestFixtureTearDown).

Before each test in the fixture is run the database schema is (re-) created and the virtual Before_each_test method is called. After each test in the fixture is finished the virtual After_each_test method is called. The two virtual methods can (but must not necessarily) be overridden in a child class.

All our test fixtures we implement will derive from this base class.

Filling the database with test data

To be able to test the loading behavior of NHibernate we need some test data in our database. We create this test data every time a test is run (just after the database schema is re-created). We add a new class Order_Fixture to our test project and inherit from the TestFixtureBase base class. Then we override the Before_each_test method and call a helper method which creates our initial data. We create just the absolute minimum of data we need (again -->DRY). That is: one customer placing one order with two order lines.

using System;

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Criterion;

using NHibernate.SqlCommand;

using NUnit.Framework;

using Order=LazyLoadEagerLoad.Domain.Order;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class Order_Fixture : TestFixtureBase

{

private Order _order;

protected override void Before_each_test()

{

base.Before_each_test();

CreateInitialData();

}

private void CreateInitialData()

{

// create a single customer and an order with two order lines for this customer

var customer = new Customer {CompanyName = "IBM"};

var line1 = new OrderLine {Amount = 5, ProductName = "Laptop XYZ"};

var line2 = new OrderLine {Amount = 2, ProductName = "Desktop PC A100"};

_order = new Order

{

OrderNumber = "o-100-001",

OrderDate = DateTime.Today,

Customer = customer

};

_order.OrderLines.Add(line1);

_order.OrderLines.Add(line2);

using (ISession session = SessionFactory.OpenSession())

using (ITransaction transaction = session.BeginTransaction())

{

session.Save(customer);

session.Save(_order);

transaction.Commit();

}

}

}

}

The CreateInitialData method is run before each test. With this we guarantee that each test is side effects free.

Verifying the default behavior - Lazy Loading

When loading an order entity from database the default behavior of NHibernate is to lazy load all associated objects of the order entity. Let's write a test to verify this. For the verification we use a utility class provided by NHibernate (NHibernateUtil) which can test whether an associated object or object collection is initialized (i.e. loaded) or not. The class can also force the initialization of an un-initialized relation.

[Test] public void Customer_and_OrderLines_are_not_loaded_when_loading_Order() { Order fromDb; using (ISession session = SessionFactory.OpenSession()) fromDb = session.Get<Order>(_order.Id); Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer)); Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines)); }

The test succeeds and NHibernate generates SQL similar to this one

SELECT order0_.Id as Id0_0_, order0_.OrderNumber as OrderNum2_0_0_, order0_.OrderDate as OrderDate0_0_, order0_.CustomerId as CustomerId0_0_ FROM Orders order0_ WHERE order0_.Id='15bca5b3-2771-4bee-9923-85bda66318d8'

Now we have a problem: If we want to access the order line items (after the session has been closed) we get an exception. Since the session is closed NHibernate cannot lazily load the order line items for us. We can show this behavior with the following test method

[Test] [ExpectedException(typeof(LazyInitializationException))] public void Accessing_customer_of_order_after_session_is_closed_throws() { Order fromDb; using (ISession session = SessionFactory.OpenSession()) fromDb = session.Get<Order>(_order.Id); // trying to access the Customer of the order, will throw exception // Note: at this point the session is already closed string name = fromDb.Customer.CompanyName; }

Note: the above test only succeeds if the method throws the expected exception of type LazyInitializationException. And this is just what we want to show!

Another problem is the n+1 select statements problem. If we access the order line items after loading the order we generate a select statement for each line item we access. Thus if we have n line items and want to access them all we generate one select statement for the order itself and n select statements for all line items (result: n+1 select statements). This can make our data fetching rather slow and put a (unnecessary) burden onto our database.

We can simulate this behavior with this test method

[Test] public void Show_n_plus_1_select_behavior() { using (ISession session = SessionFactory.OpenSession()) { var fromDb = session.Get<Order>(_order.Id); int sum = 0; foreach (var line in fromDb.OrderLines) { // just some dummy code to force loading of order line sum += line.Amount; } } }

NHibernate will generate SQL similar to the following

SELECT order0_.Id as Id3_0_, order0_.OrderNumber as OrderNum2_3_0_, order0_.OrderDate as OrderDate3_0_, order0_.Customer as Customer3_0_ FROM Orders order0_ WHERE order0_.Id='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a' SELECT orderlines0_.OrderId as OrderId1_, orderlines0_.Id as Id1_, orderlines0_.Id as Id4_0_, orderlines0_.Amount as Amount4_0_, orderlines0_.ProductName as ProductN3_4_0_ FROM OrderLine orderlines0_ WHERE orderlines0_.OrderId='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a'

This time we have been lucky! NHibernate has automatically generated an optimized query for us and has loaded the 2 order line items in one go. But this is not always the case! Imagine having a collection with several 100 items and you only need to access one or two of them. It would be a waste of resources to always load all items.

But fortunately we have a solution for these kind of problems with NHibernate. It's called eagerly loading.

Eagerly loading with the NHibernateUtil class

If you know you need have access to related objects of the order entity you can use the NHibernateUtil class to initialize the related objects (that is: to fetch them from the database). Have a look at this test methods

[Test]

public void Can_initialize_customer_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.Customer);

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

[Test]

public void Can_initialize_order_lines_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.OrderLines);

}

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

With this utility class you can initialize single objects as well as collection of objects. In each case NHibernate will send 2 select statements to the database. One to select the order and one to initialize the related object(s).

Eagerly loading with HQL

If you know that you want to load all order items of a given order then you can tell NHibernate to do so and eagerly load all order lines together with the order in one go. The following test method shows how you can formulate a HQL query which not only loads the order but also the associated customer and order lines.

[Test]

public void Can_eagerly_load_order_aggregate_with_hql_query()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

string sql = "from Order o" +

" inner join fetch o.OrderLines" +

" inner join fetch o.Customer" +

" where o.Id=:id";

fromDb = session.CreateQuery(sql)

.SetGuid("id", _order.Id)

.UniqueResult<Order>();

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

The resulting sql generated by NHibernate is then similar to this one

select order0_.Id as Id0_0_, orderlines1_.Id as Id1_1_, customer2_.Id as Id2_2_, order0_.OrderNumber as OrderNum2_0_0_, order0_.OrderDate as OrderDate0_0_, order0_.CustomerId as CustomerId0_0_, orderlines1_.Amount as Amount1_1_, orderlines1_.ProductName as ProductN3_1_1_, customer2_.CompanyName as CompanyN2_2_2_, orderlines1_.OrderId as OrderId0__, orderlines1_.Id as Id0__ from Orders order0_ inner join OrderLine orderlines1_ on order0_.Id=orderlines1_.OrderId inner join Customer customer2_ on order0_.CustomerId=customer2_.Id where order0_.Id='409ebd99-3206-459b-bfed-6df989284da9'

NHibernate has created an SQL select statement which joins the 3 tables involved, namely Orders, Customer andOrderLine. The returned (flat) set of records is then used by NHibernate to build up the object tree with the order entity as a root.

Aggregates in the Domain

DDD defines the concept of aggregates. A short definition of an aggregate is "A cluster of associated objects that are treated as a unit for the purpose of data changes.". An aggregate always has a root. In this context we can define the following aggregate in our domain

The order entity is the root and the order lines belong to the aggregate (can be regarded as children of the root). When creating a new order or changing an existing one we only want to modify either the order itself or its order lines. We certainly do not want to change the customer entity because this would be a completely different use case and does not belong to the order management use case.

So, when dealing with aggregates we often want to load the complete aggregate in one go! This is the perfect example for using eager loading techniques.

Summary

I have introduced the concept of lazy loading as provided by NHibernate. I have discussed the consequences and shown how to avoid negative side effects by using different techniques of so called eager loading.

Lazy loading - eager loading

gabriel.schenker — Sat, 06 Sep 2008 22:02:06 GMT
Revision 3 posted to How to by gabriel.schenker on 06/09/2008 07:02:06 p.m.

Lazy loading - eager loading

In this article I want to discuss the lazy loading mechanism provided by NHibernate. It is recommended for maximum flexibility to define all relations in your domain as lazy loadable. This is the default behavior of NHibernate since version 1.2. But this can lead to some undesired effects if querying your data. Let's discuss these effects and how to avoid them.

In my previous posts I showed how to prepare your system for NHibernate and how to implement a first NHibernate base application. This post is based on those two articles.

The Domain

Let's first define a simple domain. It shows part of an order entry system. I keep this model as simple as possible (a real domain model would be more complex) but it contains all aspects we want to discuss in this post. Below is the class diagram of our model

We have an order entity which can be placed by a customer entity. Each order can have many order line entities. Each of the three entity types is uniquely identified by a property Id (surrogate key).

The Mapping Files

We have to write one mapping file per entity. It is recommended that you always have one mapping per file. Don't forget to set the Build Action of each mapping file to Embedded Resource. People often tend to forget it and the subsequent errors raised by NHibernate are not always obvious. Also do not forget to give the mapping files the correct name, that is *.hbm.xml where * denotes the placeholder for the entity name.

The mapping for the Order entity might be implemented as follows

<?xml version="1.0" encoding="utf-8" ?>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"

assembly="LazyLoadEagerLoad"

namespace="LazyLoadEagerLoad.Domain">

<class name="Order" table="Orders">

<id name="Id">

<generator class="guid"/>

</id>

<property name="OrderNumber"/>

<property name="OrderDate"/>

<many-to-one name="Customer" />

<set name="OrderLines" cascade="all-delete-orphan" >

<key column="OrderId"/>

<one-to-many class="OrderLine"/>

</set>

</class>

</hibernate-mapping>

<style type="text/css"></style>
Analogous you can implement the mappings for the Customer entity

<?xml version="1.0" encoding="utf-8" ?>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"

assembly="LazyLoadEagerLoad"

namespace="LazyLoadEagerLoad.Domain">

<class name="Customer">

<id name="Id">

<generator class="guid"/>

</id>

<property name="CompanyName"/>

</class>

</hibernate-mapping>

<style type="text/css"></style>
and finally the mapping for the OrderLine entity.

<?xml version="1.0" encoding="utf-8" ?>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"

assembly="LazyLoadEagerLoad"

namespace="LazyLoadEagerLoad.Domain">

<class name="OrderLine">

<id name="Id">

<generator class="guid"/>

</id>

<property name="Amount"/>

<property name="ProductName"/>

</class>

</hibernate-mapping>

<style type="text/css"></style>

Testing the Mapping

To test the mapping we use the following test method

using LazyLoadEagerLoad.Domain;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class GenerateSchema_Fixture

{

[Test]

public void Can_generate_schema()

{

var cfg = new Configuration();

cfg.Configure();

cfg.AddAssembly(typeof(Order).Assembly);

new SchemaExport(cfg).Execute(false, true, false, false);

}

}

}

<style type="text/css"></style>
First we create a new instance of the NHibernate Configuration class and tell it to configure itself. Since we don't provide any explicit configuration here in the code NHibernate looks out for an adequate configuration file. I have included such a file (called hibernate.cfg.xml) in my project. Please consult this previous post for further details about the configuration file.
Testing the Loading Behavior of NHibernate

Defining a base class for our tests

To avoid repetitive task (DRY principle) we implement the following base class.

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Cfg;

using NHibernate.Tool.hbm2ddl;

using NUnit.Framework;

namespace LazyLoadEagerLoad.Tests

{

public class TestFixtureBase

{

private Configuration _configuration;

private ISessionFactory _sessionFactory;

protected ISessionFactory SessionFactory

{

get { return _sessionFactory; }

}

[TestFixtureSetUp]

public void TestFixtureSetUp()

{

_configuration = new Configuration();

_configuration.Configure();

_configuration.AddAssembly(typeof(Customer).Assembly);

_sessionFactory = _configuration.BuildSessionFactory();

}

[TestFixtureTearDown]

public void TestFixtureTearDown()

{

_sessionFactory.Close();

}

[SetUp]

public void SetupContext()

{

new SchemaExport(_configuration).Execute(false, true, false, false);

Before_each_test();

}

[TearDown]

public void TearDownContext()

{

After_each_test();

}

protected virtual void Before_each_test()

{ }

protected virtual void After_each_test()

{ }

}

}

When the test fixture is started, the base class configures NHibernate and creates a session factory (TestFixtureSetUp). When the whole test fixture is ended the session factory is closed (TestFixtureTearDown).

Before each test in the fixture is run the database schema is (re-) created and the virtual Before_each_test method is called. After each test in the fixture is finished the virtual After_each_test method is called. The two virtual methods can (but must not necessarily) be overridden in a child class. <style type="text/css"></style>

All our test fixtures we implement will derive from this base class.

Filling the database with test data

To be able to test the loading behavior of NHibernate we need some test data in our database. We create this test data every time a test is run (just after the database schema is re-created). We add a new class Order_Fixture to our test project and inherit from the TestFixtureBase base class. Then we override the Before_each_test method and call a helper method which creates our initial data. We create just the absolute minimum of data we need (again -->DRY). That is: one customer placing one order with two order lines.

using System;

using LazyLoadEagerLoad.Domain;

using NHibernate;

using NHibernate.Criterion;

using NHibernate.SqlCommand;

using NUnit.Framework;

using Order=LazyLoadEagerLoad.Domain.Order;

namespace LazyLoadEagerLoad.Tests

{

[TestFixture]

public class Order_Fixture : TestFixtureBase

{

private Order _order;

protected override void Before_each_test()

{

base.Before_each_test();

CreateInitialData();

}

private void CreateInitialData()

{

// create a single customer and an order with two order lines for this customer

var customer = new Customer {CompanyName = "IBM"};

var line1 = new OrderLine {Amount = 5, ProductName = "Laptop XYZ"};

var line2 = new OrderLine {Amount = 2, ProductName = "Desktop PC A100"};

_order = new Order

{

OrderNumber = "o-100-001",

OrderDate = DateTime.Today,

Customer = customer

};

_order.OrderLines.Add(line1);

_order.OrderLines.Add(line2);

using (ISession session = SessionFactory.OpenSession())

using (ITransaction transaction = session.BeginTransaction())

{

session.Save(customer);

session.Save(_order);

transaction.Commit();

}

}

}

}

<style type="text/css"></style>

The CreateInitialData method is run before each test. With this we guarantee that each test is side effects free.

Verifying the default behavior - Lazy Loading

When loading an order entity from database the default behavior of NHibernate is to lazy load all associated objects of the order entity. Let's write a test to verify this. For the verification we use a utility class provided by NHibernate (NHibernateUtil) which can test whether an associated object or object collection is initialized (i.e. loaded) or not. The class can also force the initialization of an un-initialized relation.

[Test]

public void Customer_and_OrderLines_are_not_loaded_when_loading_Order()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

fromDb = session.Get<Order>(_order.Id);

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

<style type="text/css"></style>

The test succeeds and NHibernate generates SQL similar to this one

SELECT order0_.Id as Id0_0_,

order0_.OrderNumber as OrderNum2_0_0_,

order0_.OrderDate as OrderDate0_0_,

order0_.CustomerId as CustomerId0_0_

FROM Orders order0_

WHERE order0_.Id='15bca5b3-2771-4bee-9923-85bda66318d8'

<style type="text/css"></style>

Now we have a problem: If we want to access the order line items (after the session has been closed) we get an exception. Since the session is closed NHibernate cannot lazily load the order line items for us. We can show this behavior with the following test method

[Test]

[ExpectedException(typeof(LazyInitializationException))]

public void Accessing_customer_of_order_after_session_is_closed_throws()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

fromDb = session.Get<Order>(_order.Id);

// trying to access the Customer of the order, will throw exception

// Note: at this point the session is already closed

string name = fromDb.Customer.CompanyName;

}

Note: the above test only succeeds if the method throws the expected exception of type LazyInitializationException. And this is just what we want to show!<style type="text/css"></style>

Another problem is the n+1 select statements problem. If we access the order line items after loading the order we generate a select statement for each line item we access. Thus if we have n line items and want to access them all we generate one select statement for the order itself and n select statements for all line items (result: n+1 select statements). This can make our data fetching rather slow and put a (unnecessary) burden onto our database.

We can simulate this behavior with this test method

[Test]

public void Show_n_plus_1_select_behavior()

{

using (ISession session = SessionFactory.OpenSession())

{

var fromDb = session.Get<Order>(_order.Id);

int sum = 0;

foreach (var line in fromDb.OrderLines)

{

// just some dummy code to force loading of order line

sum += line.Amount;

}

}

}

NHibernate will generate SQL similar to the following<style type="text/css"></style>

SELECT order0_.Id as Id3_0_,

order0_.OrderNumber as OrderNum2_3_0_,

order0_.OrderDate as OrderDate3_0_,

order0_.Customer as Customer3_0_

FROM Orders order0_

WHERE order0_.Id='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a'

SELECT orderlines0_.OrderId as OrderId1_,

orderlines0_.Id as Id1_,

orderlines0_.Id as Id4_0_,

orderlines0_.Amount as Amount4_0_,

orderlines0_.ProductName as ProductN3_4_0_

FROM OrderLine orderlines0_

WHERE orderlines0_.OrderId='5b2dbcb7-d0bf-4c53-86aa-8cd40cb5061a'

<style type="text/css"></style>
This time we have been lucky! NHibernate has automatically generated an optimized query for us and has loaded the 2 order line items in one go. But this is not always the case! Imagine having a collection with several 100 items and you only need to access one or two of them. It would be a waste of resources to always load all items.

But fortunately we have a solution for these kind of problems with NHibernate. It's called eagerly loading.

Eagerly loading with the NHibernateUtil class

If you know you need have access to related objects of the order entity you can use the NHibernateUtil class to initialize the related objects (that is: to fetch them from the database). Have a look at this test methods

[Test]

public void Can_initialize_customer_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.Customer);

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

[Test]

public void Can_initialize_order_lines_of_order_with_nhibernate_util()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

fromDb = session.Get<Order>(_order.Id);

NHibernateUtil.Initialize(fromDb.OrderLines);

}

Assert.IsFalse(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

<style type="text/css"></style>

With this utility class you can initialize single objects as well as collection of objects. In each case NHibernate will send 2 select statements to the database. One to select the order and one to initialize the related object(s).

Eagerly loading with HQL

If you know that you want to load all order items of a given order then you can tell NHibernate to do so and eagerly load all order lines together with the order in one go. The following test method shows how you can formulate a HQL query which not only loads the order but also the associated customer and order lines.

[Test]

public void Can_eagerly_load_order_aggregate_with_hql_query()

{

Order fromDb;

using (ISession session = SessionFactory.OpenSession())

{

string sql = "from Order o" +

" inner join fetch o.OrderLines" +

" inner join fetch o.Customer" +

" where o.Id=:id";

fromDb = session.CreateQuery(sql)

.SetGuid("id", _order.Id)

.UniqueResult<Order>();

}

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.Customer));

Assert.IsTrue(NHibernateUtil.IsInitialized(fromDb.OrderLines));

}

<style type="text/css"></style>

The resulting sql generated by NHibernate is then similar to this one

select order0_.Id as Id0_0_, orderlines1_.Id as Id1_1_, customer2_.Id as Id2_2_, order0_.OrderNumber as OrderNum2_0_0_, order0_.OrderDate as OrderDate0_0_, order0_.CustomerId as CustomerId0_0_, orderlines1_.Amount as Amount1_1_, orderlines1_.ProductName as ProductN3_1_1_, customer2_.CompanyName as CompanyN2_2_2_, orderlines1_.OrderId as OrderId0__, orderlines1_.Id as Id0__ from Orders order0_ inner join OrderLine orderlines1_ on order0_.Id=orderlines1_.OrderId inner join Customer customer2_ on order0_.CustomerId=customer2_.Id where order0_.Id='409ebd99-3206-459b-bfed-6df989284da9'

<style type="text/css"></style>
NHibernate has created an SQL select statement which joins the 3 tables involved, namely Orders, Customer andOrderLine. The returned (flat) set of records is then used by NHibernate to build up the object tree with the order entity as a root.

Aggregates in the Domain

DDD defines the concept of aggregates. A short definition of an aggregate is "A cluster of associated objects that are treated as a unit for the purpose of data changes.". ". An aggregate always has a root. In this context we can define the following aggregate in our domain

The order entity is the root and the order lines belong to the aggregate (can be regarded as children of the root). When creating a new order or changing an existing one we only want to modify either the order itself or its order lines. We certainly do not want to change the customer entity because this would be a completely different use case and does not belong to the order management use case.

So, when dealing with aggregates we often want to load the complete aggregate in one go! This is the perfect example for using eager loading techniques.

Summary

I have introduced the concept of lazy loading as provided by NHibernate. I have discussed the consequences and shown how to avoid negative side effects by using different techniques of so called eager loading.