NHibernate - Why does Delete() call fail to delete but delete through HQL works?

Question

Considering the following code blocks, why does call to HQL work but call to delete() not work? As a background, I'm using NHibernate over IBM.Data.DB2.Iseries driver. Come to find out, journaling on the AS400 is turned off so I can't use transactions. I'm not the AS400 admin or know anything about it so I don't know if having journaling turned off (not opening transactions) is causing this problem or not. Do I absolutely need the ability to open transactions if I'm calling Delete() or other NHibernate functions?

//This Does not work - no error and no deletes
public static void Delete(Object Entity)
    {
        using (ISession session = _sessionFactory.OpenSession())
        {
            //using(ITransaction tx = session.BeginTransaction())
            //{
                session.Delete(Entity);
                //tx.Commit();                    
                session.Close();                    
            //}
        }
    }

//This does work
public static void Delete(Object Entity)
    {
        using (ISession session = _sessionFactory.OpenSession())
        {
            //commented out transaction control because throws error because
            //journaling is not turned on the AS400
            //using(ITransaction tx = session.BeginTransaction())
            //{
                session.CreateQuery("delete MyDAO p where p.MyDAOID = :MyDAOID").SetString("MyDAOID", ((MyDAO)Entity).MyDAOID.ToString()).ExecuteUpdate();                
            //}
        }
    }

Answer 1

Try calling session.Flush() after you delete, but before you close the session. And you don't need to explicitly close the session:

using (var session = ...)
{
    entity.Delete();
    session.Flush();
}

Answer 2

After delving further into this, I found that this works but why?:

public static void Delete(Object Entity)
{
    using (ISession session = _sessionFactory.OpenSession())
    {       
         MyDAO p = session.Get<MyDAO>(Entity.ID);
         session.Delete(p);
         session.Flush();                                    
    }            
}

Here is my scenario: I have previously queried for a list of objects which I populated into a Grid. For that query process, I opened/closed a session. Upon calling my delete function, I take that object and pass it into this function for a separate open/close session process. To stir things up a bit, I added the call to this new delete asking it to get the object first (the one I want deleted), then call delete. Now it sends the delete query to the database and the object is in fact deleted. Why is this?

Is this because my original query of objects was opened within a different session and then deleted in another? Does this have anything to do with the unit of work. Should I open my session for my grid, leave it open until my form closes so all deletes work inside that session? I was under the impression that sessions should be opened/closed quickly. I'm confused.