Minor Description
One problem I've had in the past is when I define a callback for a class in the modeler, but then forget to implement the callback, or misspell the callback, etc.
Cayenne should ensure that a method is implemented at compile time.
At the moment, I think the "right" way to do this is:
1) Make the superclass abstract
2) Add an abstract method in the superclass
3) If generating the subclass, generate a stub method.
This ensures that naming issues are caught at compile time.