NHibernate - Set foreign key column to null when deleting

I have two entities, EntityA and EntityB. EntityB can optionally be related to EntityA, and has a foreign key column that is nullable. When EntityA is deleted, I want the foreign key in EntityB to be set to null.

So when I delete EntityA, I'd like it to set the foreign key in any referenced EntityBs before issuing the DELETE command. I've seen NHibernate do this before "accidentally", and now that I actually want it to do that, I can't seem to get it right. The best I've been able to do is delete EntityB once it is orphaned, which is not what I want. Of course, I could set the foreign key constraint in SQL Server to set the column to null, but I feel like NHibernate should be able to do this. Similarly, I could loop through all EntityB referenced by the EntityA to be deleted, and set them to null. Again, why should I have to?

Here are my entities and mappings:

public class EntityA : Entity // Entity contains the ID property and implements GetHashCode() and Equals()
{
    // irrelevant properties

    public virtual IList<EntityB> EntityBs { get; protected set; }
}

public class EntityB : Entity
{
    // irrelevant properties
    public virtual EntityA EntityA { get; set; }
}


public class EntityAMap: ClassMap<EntityA>
{
    public EntityAMap()
    {
         HasMany(c => c.EntityBs)
             .ForeignKeyConstraintName("FK_EntityA_EntityB")
         .KeyColumn("EntityA_Id")
             .Inverse()
             .Cascade.None(); // i've tried other cascade settings with little luck
    }   
}

public class EntityBMap: ClassMap<EntityB>
{
    public EntityBMap()
    {
         References(c => c.EntityA)
             .Nullable()
             .Column("EntityA_Id")
             .ForeignKey("FK_EntityA_EntityB")
             .Index("IX_EntityB_EntityA_Id")
             .Cascade.None();
    }   
}

I then delete like this:

var entityA = Reposito开发者_如何转开发ry.Get(idToDelete);
// entityA.EntityBs.Clear(); // tried this, no affect
Repository.Remove(entityA);

Repository.Flush(); // is it possible this isn't working because I'm missing a Tx?

The result is a foreign key constraint violation, because EntityB.EntityA_Id is not being nulled out.

You need to do something like:

entityA.EntityBs.ToList().ForEach(b => b.EntityA = null );

Repository.Remove(entityA);
Repository.Flush();

If any B's are still referencing A you can't delete A, especially with no cascading going on.

You have to set all cascades to none and then .inverse() in EntityBMap. Please give me feedback if it works.

Mariusz