Thanks for the assistance!
This is what I finally used to get the desired behavior (after
updating to 0.4.5):
session.query(Detection).with_polymorphic('*').options(eagerload(Detection.sensor)).all()
Chris G.
At 05:38 PM 4/3/2008, you wrote:
>On Apr 3, 2008, at 4:37 PM, Chris Guin wrote:
>
> >
> > eagerload() appears not to work when employed on queries to classes
> > that have subclasses using joined table inheritance. I found a
> > thread suggesting that, for such cases, contains_eager() would be
> > better, although you have to build the statement yourself from which
> > to query.
> >
> > When my table structure was simpler, this worked perfectly. But I
> > have since added a new base class from which pretty much all of the
> > other tables inherit, with the result that, when I use contains_eager
> > to load a "sensor" into a "detection" (a detection has-a sensor, but
> > both sensor and detection inherit from clips_object), SQLAlchemy
> > loads a copy of the detection object itself into the "sensor" slot
> > (the object even has the same memory address). Any idea what might
> > be causing this behavior?
> >
> > Here are the statements and queries I'm using:
> >
> > sensor_alias = sensor \
> > .join(device, device.c.item_id==sensor.c.item_id) \
> > .join(clips_object,
> > device.c.item_id==clips_object.c.clips_instance_name) \
> > .select(use_labels=True).alias()
> >
> > eager_detection = clips_object \
> > .join(event, event.c.event_id ==
> > clips_object.c.clips_instance_name) \
> > .join(detection, detection.c.event_id == event.c.event_id) \
> > .join(sensor_alias,
> > sensor_alias.c.sensor_item_id==detection.c.fk_sensor_id) \
> > .outerjoin(aspect_detection, aspect_detection.c.event_id ==
> > detection.c.event_id) \
> > .outerjoin(rf_detection, rf_detection.c.event_id ==
> > detection.c.event_id) \
> > .select(use_labels=True)
> >
> > dets =
> > session
> > .query
> > (Detection
> > ).options
> > (contains_eager('sensor')).from_statement(eager_detection).all()
> >
>
>If sensor_alias represents the rows used to load Sensor objects,
>contains_eager should say: contains_eager('sensor',
>alias=sensor_alias).
>
>Im also not entirely sure why the from_statement is needed. Since you
>are loading Detection which directly links to Sensor, there shouldn't
>be any issue with eagerloading sensor. In any case, if you run the
>trunk, you should be able to eagerload subclass collections, such as:
>
>sess
>.query
>(Clip
>).with_polymorphic(Detection).options(eagerload(Detection.sensor)).all()
>
>
>
>
>
>
>
>
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