[SQLObject] Problems with Inheritence

[Jeff W. <je...@me...>]

While working on the identity framework for TurboGears, I've been  
trying to come up with a clean way to allow developers to provide  
their own identity model classes. One thought was to load the name of  
the developer's preferred User class and instantiate that instead of  
the default User class.

So this means I have the following model:

class User(SQLObject):
     class sqlmeta:
         table="user_table"
     # meaningful columns left out for brevity
     groups=RelatedJoin( "Group", intermediateTable="user_group",
                         joinColumn="user_id", otherColumn="group_id" )

class Group(SQLObject):
     class sqlmeta:
         table="group_table"
     # meaningful group info left out for brevity
     users=RelatedJoin( "User", intermediateTable="user_group",
                        joinColumn="group_id", otherColumn="user_id" )

All works great so far. But then I add an override for the User class  
to the config file to specify MyUser instead of User. MyUser is  
defined as:

class MyUser(User):
     # additional package specific stuff

However, when I instantiate a MyUser object and add it to a group,  
attempting to retrieve the list of groups for that object results in  
an Exception:

miles:~/Sites/turbo/cms> tg-admin shell
Python 2.4.1 (#2, Mar 31 2005, 00:05:10)
[GCC 3.3 20030304 (Apple Computer, Inc. build 1666)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
 >>> u= MyUser.get(1)
 >>> u
<MyUser 1 userId='jeff' password='xxxx'  
emailAddress='je...@me...' displayName='Jeff Watkins'  
created='datetime.datetime...)' age=0>
 >>> u.groups
Traceback (most recent call last):
   File "<console>", line 1, in ?
   File "<string>", line 1, in <lambda>
IndexError: list index out of range
 >>>

Now I suppose this is caused by the join relating Users and Groups,  
but I would have expected (wrongly, I guess) that a relation between  
MyUser and Groups would automatically be created by inheriting the  
RelatedJoin in User.

What am I missing here?

--
Jeff Watkins
http://metrocat.org/

'I know about people who talk about suffering for the common good.  
It's never bloody them! When you hear a man shouting "Forward, brave  
comrades!" you'll see he's the one behind the bloody big rock and the  
one wearing the only really arrow-proof helmet!'
-- Rincewind gives a speech on politics. (Terry Pratchett,  
Interesting Times)