[Zope-dev] Re: [ZODB-Dev] Schema migration, rename class

[Syver Enstad]

Jeremy Hylton <jeremy at zope.com> writes:

> On Wed, 2004-03-31 at 09:19, Syver Enstad wrote:
> > I am looking for good resources on schema migration with ZODB. 
> > 
> > http://www-106.ibm.com/developerworks/linux/library/l-pypers.html
> > 
> > Shows some of the techniques (the article is about Pickling) The
> > article describes how to rename a class by changing the self.__class__
> > to the renamed class in __setstate__ but this doesn't seem to work.
> 
> (I haven't followed the link yet, but ...)  You can't change the class
> of a persistent object, although it may seem like you can because you
> can assign to __class__.  

I am not really interested in changing the class. I am interested in
renaming it. Are there any resources on schema evolution/migration
with ZODB, I have googled quite a bit but so far haven't come up with
anything other than the link above which only seems to work with
pickles.

> The problem is that persistent references
> contain the class and oid of the object.  So you can change __class__,
> but the next time the object is loaded it will get whatever class its
> referrer thinks it has.