Dieter Maurer wrote:

Syver Enstad wrote at 2005-11-7 11:51 +0100:
In ZODB 3.2 I can replace the _classFactory method on DB and locate the
renamed/moved class by other means (a lookup table that maps old module
classname pairs to another class in another module). If I change
attributes of the persistent instance it will be saved with the new
class name instead of the old.

I can't get this strategy to work under 3.5.1. It seems to work okay as
long as I use the custom classFactory method (not _classFactory as in
3.2) but 3.5.1 doesn't seem to update the modulename, classname when I
save the instance.

What I want to do is just update the persistent instance so that it will
load from the new module/ new class after I have done a one time update
of the database.

I fear this will not work.

For efficiency reasons, the class designator (usually a
module, classname tuple) is stored both in the object itself
and in persistent references. While you will be able
to modify the object's class the persistent references will
only change when the containers are stored into the ZODB.

Okay, so as far as I can see one has to either install a custom classfactory method on the DB instance that maps from old to new locations or hack sys.modules to refer to the new location by the old name.

What I don't like is that this will break for the following case as far as I see.

firstModule.First renamed ->  secondModule.Second

Some time later in the database life:
New class: firstModule.First.
Will be hidden by the machinery that hacks in secondModule.Second under the old name firstModule.First.
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