NHibernate SaveOrUpdate Child Collection Not Updated With Identity Ids

Question

I am clearly missing something (hopefully obvious), and I have had no luck with Google so far.

I have a Parent-Child relationship mapped as follows

Simplified Parent Map

  public sealed class ParentMap : ClassMap<ParentEntity>
  {
    public ParentMap()
    {
      Table("Parent");
      Component(x => x.Thumbprint);
      Id(x => x.Id).GeneratedBy.Identity();

      Map(x => x.ServeralNotNullableProperties).Not.Nullable();

      HasMany(x => x.Children).KeyColumn("ChildId")
                              .Inverse()
                              .LazyLoad()
                              .Cascade
                              .AllDeleteOrphan();

      References(x => x.SomeUnrelatedLookupColumn).Column("LookupColumnId").Not.Nullable();
    }
  }

Simplified Child Map

  public sealed class ChildMap : ClassMap<ChildEntity>
  {
    public ChildMap()
    {
      Table("Child");
      Component(x => x.Thumbprint);
      Id(x => x.Id).GeneratedBy.Identity();

      Map(x => x.MoreNotNullableProperties).Not.Nullable();

      References(x => x.Parent).Column("ParentId").Not.Nullable();
    }
  }

Simplified Service Method Steps

I then have a service method that retrieves Parent and adds a new Child via some domain method. The underlying NHibernate code boils down to:

1) Session Opened on WCF AfterReceiveRequest (IDispatchMessageInspector)

_sessionFactory.OpenSession();

2) Retrieve existing instance of parent via .Query

_session.Query<ParentEntity>()
        .Where(item => item.Id == parentId)
        .Fetch(item => item.SomeLookupColumn)
        .First();

3) Add new 'Child' entity to 'Parent' via domain object method such as...

public ChildEntity CreateChild()
{
  var child = new ChildEntity{ Parent = this };

  Children.Add(child);

  return child;
}

4) Ultimately calls SaveOrUpdate on 'Parent' entity.

 // ChildEntity Id is 0
 _session.SaveOrUpdate(parentEntity)
 // Expect ChildEntity Id to NOT be 0

Note: Use of SaveOrUpdate Does persist changes to database; use of Merge results in TransientObjectException mentioned below.

5) Finally, transaction committed on WCF BeforeSendReply (IDispatchMessageInspector)

 _session.Commit();

The Problem

Typically when an entity is saved, after the call to SaveOrUpdate, the Id of said entity refects the Identity generated by the INSERT statement. However, when I add a new child entity to an existing parent, the associated entity in Children does not get assigned an Id. I need to pass this Id back to the caller so subsequent calls result in UPDATES and not additional INSERTS.

Why is NHibernate not updating the underlying entity? Do I explicitly have to call SaveOrUpdate on the child (that sucks if that is the case)?

Any thoughts on the matter greatly appreciated. Thanks!

EDIT I should note, that the new child entity IS being saved as expected; I just don't get back the Id assigned.

UPDATE Tried switching to .Merge(~) as suggested by Michael Buen below; resulting in a TransientObjectException telling me to explicitly save my modified child entity before calling merge. I also experimented with .Persist(~) to no avail. Any additional insight greatly appreciated.

object is an unsaved transient instance - save the transient instance before merging: My.NameSpace.ChildEntity

Answer 1

You could call session.Flush(), which performs the inserts on the database. This is not ideal because of the impact to performance.