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[1.8.x] Fixed #24019 -- Fixed inaccurate docs about GenericRelation not supporting aggregation. 

This works at least as far back as Django 1.6 according to the test
added in refs #10870.

Backport of e19bd086d6 from master
This commit is contained in:
Tim Graham 2015-10-29 17:38:05 -04:00
parent 052bd3f7e3
commit 5adeb41025
1 changed files with 4 additions and 10 deletions
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14
docs/ref/contrib/contenttypes.txt
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@ -475,18 +475,12 @@ signal.
Generic relations and aggregation
---------------------------------
:doc:`Django's database aggregation API </topics/db/aggregation>`
doesn't work with a
:doc:`Django's database aggregation API </topics/db/aggregation>` works with a
:class:`~django.contrib.contenttypes.fields.GenericRelation`. For example, you
might be tempted to try something like::
can find out how many tags all the bookmarks have::
Bookmark.objects.aggregate(Count('tags'))
This will not work correctly, however. The generic relation adds extra filters
to the queryset to ensure the correct content type, but the
:meth:`~django.db.models.query.QuerySet.aggregate` method doesn't take them
into account. For now, if you need aggregates on generic relations, you'll
need to calculate them without using the aggregation API.
>>> Bookmark.objects.aggregate(Count('tags'))
{'tags__count': 3}
.. module:: django.contrib.contenttypes.forms