This was a long thread, and I may have missed some points already
made. Let me try to summarize this discussion and add my comments to
it. There are two aspects of the "vertical inheritance relationship":
1. Specifying the join semantics for non-trivial PK-to-PK mapping
(such as compound keys).
2. Specifying delete rules.
I am with Ari on (1) - it is in the Cayenne philosophy to map things
explicitly, so that various weird legacy schemas can still be mapped.
I am with Craig on (2) - if a user expects to delete a record from a
subclass table without deleting a record in a superclass table, this
situation should not be mapped as inheritance, as it breaks the ORM
model at a fundamental level (an object is deleted, but some of its
properties still remain persistent - BAD).
With this in mind we do not need an inheritance ObjRelationship, but
we may use a DbRelationship to store join semantics (anybody
mentioned that already??). Another nice side effect of it is that
such relationship is not a part of the object model (ObjRelationship
would've been an object property). So there is nothing artificial
about such mapping, and no new concepts are needed in Cayenne to map it.
Andrus
