Hello,
I'm changing the names a bit, for privacy reasons (if you need more
details please say so), but I have the following models:
class Event(BaseModel):
name = db.StringProperty(required=True)
...
class EventObservation(BaseModel):
event = db.ReferenceProperty(Event,
collection_name='observations')
accuracy = db.FloatProperty(required=True)
...
For every Event instance in the datastore I have at least one
EventObservation. I also have the following index:
- kind: EventObservation
properties:
- name: event
- name: accuracy
direction: desc
The dashboard for the app says that the index is computed ("Serving").
But in a scheduled task which goes through the EventObservation's of
some Event's, the app got an exception because no EventObservation was
returned for one of the Event's, even though there is one. The
relevant code is:
q = db.Query(EventObservation).filter('event =', event).order("-
accuracy")
obs = q.get()
if obs.accuracy > 0.0: # assumed there always is an EventObservation
...
Using the remote API and a local shell, I found the following two
behaviors:
# with order("-accuracy") there are no results
my-app> q2 = db.Query(EventObservation).filter('event =',
a_specific_event).order("-accuracy")
my-app> q2.count()
0L
# without the order the single observation is correctly returned
my-app> q2 = db.Query(EventObservation).filter('event =',
a_specific_event)
my-app> q2.count()
1L
# the EventObservation has good data
my-app> obs = q2.get()
my-app> obs
EventObservation(**{'event': datastore_types.Key.from_path(u'Event',
138001L, _app=u'my-app'), 'accuracy': 89.0})
My question is the following. Given that I have an index for "event /
accuracy", and that the index is "Serving", what can be the reason
that a particular EventObservation is not being returned, since it
exists? Could it be that the indexing process missed it? Is it because
there is a single EventObservation for that Event? Am I relying on a
wrong type of consistency? Am I doing something else wrong?
(BTW, the index was generated by uploading a new index.yaml. Since
then no more Event's or EventObservations were added to the datastore,
which makes it even stranger. I haven't tried regenerating the
indexes, since if this happened to be an app engine bug I guess you
might want to try ascertaining the cause?)
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