[Zope3-Users] Extending interfaces and implementations

[Behrang Dadsetan]

Hi,

when a class is augumented of a new attribute, my understanding is
that the instances created with the older version of the class will
not have that attribute. Will the interfaces and methods that are also
updated to reflect the new attribute will fail on older instances?

Is there any migration tools used to "update" old instances? Does one
have to rewrite it every time one does an upgrade? I guess one could
decide to populate that attribute with its default value like most
systems tend to do.. but what methods would I have handy?

Is a completely different strategy used, like versioning of classes
with templates and class method implementations linked to the specific
version of the instance's class?

Maybe the problem I am talking about only concerns ZODB based
repositories of objects and not RDBs. Does everyone use RDBs?

Also how difficult would it be to add a runtime "reload" of zcml
configurations or python modules? Was it a design decision not to have
this handy, or would such a feature be interesting for the community?

Thanks
Ben.