#28296: Add support for aggregation through subqueries
-------------------------------------+-------------------------------------
Reporter: László Károlyi | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Diederik van der Boor):
> ... either make aggregate return a lazy object that Subquery can deal
with (right now it returns a dict on call)
I second that! It would make subqueries much easier to use.
A lazy dict or `AggregateResult` doesn't have to be too complicated.
Providing `__getitem__`, `__contains__`, etc.. like `UserDict` would do
the trick.
The same could happen with `.count()`. By letting it return a lazy
`CountResult` object that casts to an int, it doesn't change the existing
code, but also offers some `.query` attribute that `Subquery()` can use.
This would allow things like:
{{{
Performance.objects.annotate(
reserved_seats=Subquery(
SeatReservation.objects.filter(
performance=OuterRef(name='pk'), status__in=TAKEN_TYPES
).aggregate(Count('pk'))
)
)
}}}
Or even:
{{{
Performance.objects.annotate(
reserved_seats=Subquery(
SeatReservation.objects.filter(
performance=OuterRef(name='pk'), status__in=TAKEN_TYPES
).count()
)
)
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/28296#comment:7>
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