One-to-one & foreign key & entity inheritance problem

bfreis · **Joined:** Wed Sep 09, 2009 6:05 am **Posts:** 2

Hello, I have a problem with a mapping.

My (simplified) domain model is as follows (C# code):

Code:

     public abstract class Entity<TEntity, TId>
         where TEntity : Entity<TEntity, TId>
     {
         public virtual TId Id { get; protected set; }
         public override bool Equals(object obj)...
         ...
     }
     
     public class EntityA<EntityA, long> : Entity<EntityA, long>
     {
         public virtual EntityB B { get; private set; }
         /* ... */
     }
     
     public class EntityB<EntityA, long> : Entity<EntityB, long>
     {
         /* ... */
     }

Here I have a one-to-one relationship between EntityA and EntityB, ie, each EntityA must contain exactly one EntityB. I cannot just "copy" the fields of EntityB into EntityA. They must be 2 separate entites, and in the database they must be 2 separate tables.

So, I did the following mapping (using the Fluent NHibernate interface):

Code:

     public class EntityAMap : ClassMap<EntityA>
     {
         public EntityAMap()
         {
             Id(x => x.Id);
             HasOne(x => x.B)
                 .Cascade.All();
             /* ... */
         }
     }
     
     public class EntityBMap : ClassMap<EntityB>
     {
         public EntityBMap()
         {
             Id(x => x.Id)
                 .GeneratedBy.Foreign("Id");
             /* ... */
         }
     }

Then I create a valid entityA, ready to be saved:

Code:

     var entityA = EntityAFactory.CreateNewValidEntityA();
     session.SaveOrUpdate(entityA);

The problem is that NHibernate throws an exception: "Unable to resolve property: Id".

On my log (and DB) I can see that NHibernate correctly "inserted" entityA into the database, and by debuging the code I can see that it assigned the correct Id to my entityA.

Furthermore, from the stack trace, I can see that this exception was thrown when NHibernate was trying to save the "cascaded" EntityB:

Code:

     at NHibernate.Tuple.Entity.EntityMetamodel.GetPropertyIndex(String propertyName)
     at NHibernate.Tuple.Entity.AbstractEntityTuplizer.GetPropertyValue(Object entity, String propertyPath)
     at NHibernate.Persister.Entity.AbstractEntityPersister.GetPropertyValue(Object obj, String propertyName, EntityMode entityMode)
     at NHibernate.Id.ForeignGenerator.Generate(ISessionImplementor sessionImplementor, Object obj)
     ...
     at NHibernate.Impl.SessionImpl.SaveOrUpdate(String entityName, Object obj)
     at NHibernate.Engine.CascadingAction.SaveUpdateCascadingAction.Cascade(IEventSource session, Object child, String entityName, Object anything, Boolean isCascadeDeleteEnabled)
     at NHibernate.Engine.Cascade.CascadeToOne(Object child, IType type, CascadeStyle style, Object anything, Boolean isCascadeDeleteEnabled)
     at NHibernate.Engine.Cascade.CascadeAssociation(Object child, IType type, CascadeStyle style, Object anything, Boolean isCascadeDeleteEnabled)
     at NHibernate.Engine.Cascade.CascadeProperty(Object child, IType type, CascadeStyle style, Object anything, Boolean isCascadeDeleteEnabled)
     at NHibernate.Engine.Cascade.CascadeOn(IEntityPersister persister, Object parent, Object anything)
     ...
     at NHibernate.Impl.SessionImpl.SaveOrUpdate(Object obj)
     at myproject...

It looks like NHibernate is having trouble to determine the foreign Id.
How can I solve this problem?

Thanks!

EDIT

I think I was misunderstanding the "GeneratedBy.Foreign". I created a property on my EntityB pointing back to my EntityA, and said that EntityB's Id is generated by EntityB.A's Id (GeneratedBy.Foreign("A")). However I still have no success. The same exception now says that NHibernate cannot access the "A" property.

mirezko · **Joined:** Tue Aug 31, 2010 10:23 am **Posts:** 1

I think you solved this, but for other users sake:

LINK: Marek Blotny's Blog - Fluent NHibernate and Inheritance Mapping

Code:

Id(x => x.Id, "CustomerID").GeneratedBy.Foreign("Customer");
Map(x => x.Demographics);
Map(x => x.ModifiedDate);
Map(x => x.Contact, "ContactID");
HasOne(x => x.Customer).Constrained();

note the most important x => x.Customer and GeneratedBy.Foreign("Customer")
(yes, there are the same Customer column, 1 lambda and 1 magic string, which is unfortunate, but necessary)

billyy2288 · **Joined:** Mon Sep 06, 2010 11:38 pm **Posts:** 1

bfreis wrote:

I think I was misunderstanding the "GeneratedBy.Foreign". I created a property on my EntityB pointing back to my EntityA, and said that EntityB's Id is generated by EntityB.A's Id (GeneratedBy.Foreign("A")). However I still have no success. The same exception now says that NHibernate cannot access the "A" property.

I also think so.