I have a question about updating the objects in a ZODB. Suppose I already have 100 objects of class A and then I modify class A adding a new attribute. Then I craete a new object of the class A and now I have two kind of instances of my class A, the old ones and the new one.

How do I update the old objects and add the new attribute to them? I can provide a default value for this attribute if that helps.

I guess changing the methods of the class A is not a problem since those are not stored in the database.

I know this is a common issue with application updates. I also know that during the development phase the best thing I can do is remove the Data.fs file and start again and that's what I'm currently doing. But I'm worried about installing the application in the client machines and two month later needing to add more fields to my content-types. If I understand correctly one of the advantages of Zope3 is the support for always-changing-applications. So how does it work in this particular situation?

Any pointer to documentation about this or to an example application that does this will be very helpful.

Thanks in advance

Lorenzo Gil
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