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Fixed #11039: documented that aggregation and generic relations don't mix. Thanks, psmith. 

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10781 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Jacob Kaplan-Moss 2009-05-14 02:38:27 +00:00
parent 5bdee2556e
commit d987b378ce
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docs/ref/contrib/contenttypes.txt
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@ -339,6 +339,21 @@ pointing at it will be deleted as well. In the example above, this means that
if a ``Bookmark`` object were deleted, any ``TaggedItem`` objects pointing at
it would be deleted at the same time.
Generic relations and aggregation
---------------------------------
:ref:`Django's database aggregation API <topics-db-aggregation`
doesn't work with a
:class:`~django.contrib.contenttypes.generic.GenericRelation`. For example, you
might be tempted to try something like::
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 ``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.
Generic relations in forms and admin
------------------------------------