diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/ref/contrib/contenttypes.txt | 14 |
1 files changed, 4 insertions, 10 deletions
diff --git a/docs/ref/contrib/contenttypes.txt b/docs/ref/contrib/contenttypes.txt index 539bba961b..6d14b88f1a 100644 --- a/docs/ref/contrib/contenttypes.txt +++ b/docs/ref/contrib/contenttypes.txt @@ -455,18 +455,12 @@ 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 |