[odb-users] Schema evolution and upward compatibility

[Christian Sell]

Hello,
 
we have a requirement that our application not only provide forward schema
migration (i.e., a newer version of the app will be able to access and migrate a
schema created with an older version), but also upward schema compatibility. By
this I mean that an older application will be able to access a newer schema and
still behave gracefully.
 
Now, I understand that this will only work if the application has been designed
with that compatibility in mind, but there are a few aspects that rely on ODB,
namely:
 
1. if we enable schema versioning and forward migration, can we tell ODB to also
accept newer schemas (without migrating of course) or will QDB simply refuse to
cooperate
2. if 1. is true, would we be able to traverse polymorphic relationships where
new classes have been defined and are referenced in the relationship? Our
expectation would be that non-mapped classes would simply be ignored.
 
example:
 
schema 1:   classA 1---N-> classB
                     classB ---subclass--> classB1
 
schema 2:   classA 1---N-> classB
                     classB ---subclass--> classB1
                     classB ---subclass--> classB2
 
now, when I traverse the relationship a->b in the app based on schema1, and the
relationship contains, say, {classB1, classB2}, I would only see {classB1}
 
thanks,
Christian