[ZODB-Dev] Class Versioning?

[Chris Spencer]

Would it be possible to support some system of class versioning in ZODB, 
to aid to handling modifications to source code? For instance, suppose 
each class definition has a __version__ attribute. Upon serialization, 
this version is saved for each instance. Then, if the class is updated, 
signified by incrementing the class's __version__, ZODB could take 
action, for example, by executing an optional __upgrade_to_x(self) in 
the new class definition.

Chris