Hello again dear list,
I have a mapped class is polymorphic with single table inheritance. I have
a function wired up to the load() SA event. The dictionary in the
InstanceState which is passed to the load event depends on whether I am
querying on the base class or a derived one, which I don't _think_ it
should be.
Here is a concrete example, which is a bit contrived - I am actually knee
deep inside mapping mutable JSON objects stored in values of HSTOREs; this
is a distilled version of the problem:
class PolyBase(Base):
name = Column(String, primary_key=True)
type = Column(String)
__mapper_args__ = {'polymorphic_on': type}
class Cake(PolyBase):
topping = Column(String)
__mapper_args__ = {'polymorphic_identity': 'Cake'}
def load_event(state, *args):
print state.dict.keys()
sqlalchemy.event.listen(Cake, 'load', load_event, raw=True, propagate=True)
Now:
> session().query(Cake).filter_by(name='mycake').one()
['date', '_sa_instance_state', 'type', 'name']
However, in a fresh session:
> session().query(PolyBase).filter_by(name='mycake').one()
['_sa_instance_state', 'type', 'name']
See 'date' is missing when I query on PolyBase, even though in both cases
state.obj is a Cake instance. I've been looking at the object loading code
in SQLAlchemy and it is rather fierce; is this expected behavior?
Either way can anyone think of a fix/workaround?
Cheers for reading this far!
- Philip
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