Question

my application has 2 entities called Event and Transaction. An Event may or may not have a transaction but can only have 1 Transaction. I thought the best way to map this was with a HasOne mapping. So far everything is fine but i want to make sure that when you delete an Event it won’t delete it if has a Transaction.

Normally on a HasMany relationship i would just set an Inverse and change Cascade to None. While Cascade exists, Inverse doesn’t and the event deletes regardless of whether it has a Transaction or not.

I’d appreciate it if someone could show me the correct way of doing this. Thanks

Answer 1

You could always create your own custom delete behaviour using a DeleteEventListener:

public class DeleteEventListener : DefaultDeleteEventListener
  {
    protected override void DeleteEntity(IEventSource session, object entity, EntityEntry entityEntry, bool isCascadeDeleteEnabled, IEntityPersister persister, ISet transientEntities)
    {
      Event event = entity as Event;
      if (event != null && event.Transaction != null) throw new Exception("You can't delete this Event! Look! It has a Transaction!");
      CascadeBeforeDelete(session, persister, entity, entityEntry, transientEntities);
      CascadeAfterDelete(session, persister, entity, transientEntities);
    }
  }

This DeleteEventListener would then need to be registered as part of your NHibernate setup configuration. Within the session factory element:

<event type="delete">
<listener class="myNamespaces.DeleteEventListener, myAssembly" />
</event> 

I haven’t tested this particular code but I have similar code in my app so I can help out if you get stuck.