Many to many - composite key and multiple session
Antoine
via web
I try to understand nHibernate and Fluent, when using Many to Many relationship.
Imagine the following tables :
- Post (id, title, content)
- Tag (id, name)
- PostTags (idTag, idPost)
PostTags have a composite key (idtag, idpost).
I want to do the following things with the NH objects :
Tag t1 = new Tag("foo").Save(); // created with a session A (always open, attached to the object)
Tag t2 = new Tag("bar").Save(); // created with a session B (always open, attached to the object)
Post p = new Post(1, "my title", "my content").Save(); // created with a session C (always open, attached to the object)
p.AddTag(t1);
t2.AddPost(p);
Assert.AreEqual(2, p.Tags.Count);
Assert.AreEqual(1, t1.Posts.Count);
Assert.AreEqual(1, t2.Posts.Count);
p.Delete(t1);
Assert.AreEqual(1, p.Tags.Count);
Can you please give me the code of :
- The hibernate entities, and the mapping (with the composity key, iset or ibags, etc).
- The method AddTag and the method AddPost (with the explanation when manipuling multi session - refresh, merge etc.).
This example will really help me to understand nHibernate. I read lot of post about nhibernate, but revolving this example will help me a lot.
Sincerely,
Antoine
Support Staff 2 Posted by James Gregory on 05 Nov, 2010 01:52 PM
What do you mean "created with a session A (always open, attached to the object)"? A session should not be attached to an object, unless I'm misunderstanding your description.
If you have an entity created with a different session as the one you're trying to save it with, you'll need to do a
session.Attach(entity)first to make the new session aware of it.3 Posted by Antoine on 05 Nov, 2010 02:15 PM
It was just an example. The goal is to understand how to manipulate entities created in different session.
The session.Attach syntax is interesting, but I don't find it (I use NH2.1). Do you mean Merge or Refresh instead of Attach ?
Thanks a lot,
Antoine
Support Staff 4 Posted by James Gregory on 05 Nov, 2010 02:26 PM
Sorry, that was my mistake. I believe the Update method will associate an entity with a session other than the one it was fetched with.