def register_dependencies(self, uowcommit):
        # many-to-many.  create a "Stub" mapper to represent the
        # "middle table" in the relationship.  This stub mapper doesnt save
        # or delete any objects, but just marks a dependency on the two
        # related mappers.  its dependency processor then populates the
        # association table.

        stub = MapperStub(self.parent, self.mapper, self.key)
        uowcommit.register_dependency(self.parent, stub)
        uowcommit.register_dependency(self.mapper, stub)
        uowcommit.register_processor(stub, self, self.parent)