I have a model with a multi-valued property, "events", and I want to filter
by a specific range of events and sort by them at the same time:
class MyModel(db.Model):
events = db.StringListProperty(indexed=True)
print MyModel.all().filter("events >=", x).filter("events <=",
y).order("events").fetch(100)
I expect the results to be sorted by whichever value in the list
property that matched the range condition (and that's how I understand the
indexs to be organized). This seems to be working as expected in the SDK,
and if I reverse the order ("-events") it returns the results in reverse as
well, which is great.
However, I'm concerned about the section below from the
documentation<https://developers.google.com/appengine/docs/python/datastore/queries>
which
states that sort orders are ignored. It's not clear to me, though, if the
sort order is ignored completely or ignored only for the "other" values in
the property list that did not match the range condition. And if it is
ignored, then how come reversing the sort oder in the code above also
reversed the order of the results I get?
Sort Orders Are Ignored on Properties with Equality Filters
One important caveat is queries with both an equality filter and a sort
order on a multi-valued property. In those queries, the sort order is
disregarded. For single-valued properties, this is a simple optimization.
Every result would have the same value for the property, so the results do
not need to be sorted further.
However, multi-valued properties may have additional values. Since the sort
order is disregarded, the query results may be returned in a different
order than if the sort order were applied. (Restoring the dropped sort
order would be expensive and require extra indices, and this use case is
rare, so the query planner leaves it off.)
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