Author: jacob
Date: 2009-05-13 21:38:27 -0500 (Wed, 13 May 2009)
New Revision: 10781
Modified:
django/trunk/docs/ref/contrib/contenttypes.txt
Log:
Fixed #11039: documented that aggregation and generic relations don't mix.
Thanks, psmith.
Modified: django/trunk/docs/ref/contrib/contenttypes.txt
===================================================================
--- django/trunk/docs/ref/contrib/contenttypes.txt 2009-05-14 02:35:16 UTC
(rev 10780)
+++ django/trunk/docs/ref/contrib/contenttypes.txt 2009-05-14 02:38:27 UTC
(rev 10781)
@@ -339,6 +339,21 @@
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
------------------------------------
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