appengine - how to get class_set on a selfreferencing polymodel?

Question

If I have

Class Base(polymodel.Model): parentItem = db.SelfReference()

SubClassA(Base): ...

SubClassB(Base): ...

SubClassA and SubClassB can be parent/childs of the other.

Id like to be able get the SubClassB items that reference SubClassA using the usual xxxx_set() method that is generated but it doesnt seem to work.

subA.subclassb_set()

I get an AttributeError 'SubClassA' object has no attrbute 'subclassb_set'

I can do SubA.base_set() fine.

Is there an alternative?

Thanks