Delete child object when parent still has reference in NHibernate

Question

I read this thread regarding my issue but still had questions.

I have two entities -- an Order and a Task. There is a one-to-many relationship between an Order and its child Tasks.

//Order.hbm.xml
<bag name="Tasks" table="Task" inverse="true" cascade="all-delete-orphan">
  <key column="OrderID" />
  <one-to-many class="Task, Orders" />
</bag>

//Task.hbm.xml
<many-to-one name="Order" column="OrderID" />

I would like to delete a Task and have NHibernate keep my Order in-sync.

My first attempt yielded the issue:

Deleted object would be re-saved by cascade

I resolved this by manually cleaning up Order's reference to Task before committing my transaction:

public void DeleteTask()
{
    NHibernateSessionManager.Instance.BeginTransaction();
    //Need to remove Order's reference to Task before deleting so that Task is not resaved.
    Task.Order.Tasks.Remove(Task);
    TaskDao.Delete(Task);
    NHibernateSessionManager.Instance.CommitTransaction();
}

It seems like this bit of code should be able to be handled by NHibernate's XML files, though. Is this a correct assumption? How would I need to change my NHibernate configurations such that when a Task is deleted the reference is automatically cleaned up for its parent Order, too?

score 3 · Accepted Answer · answered Sep 12 '12 at 12:45

Actually, since you have cascade="all-delete-orphan", you can do without the explicit Delete():

public void DeleteTask()
{
    NHibernateSessionManager.Instance.BeginTransaction();
    Task.Order.Tasks.Remove(Task);
    NHibernateSessionManager.Instance.CommitTransaction();
}

This is more DDD-ish, as you can do the changes from the model itelf without any references to NH, and then let NH's change tracking take care of the delete.

Delete child object when parent still has reference in NHibernate

1 Answers1