diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/topics/db/aggregation.txt | 13 |
1 files changed, 7 insertions, 6 deletions
diff --git a/docs/topics/db/aggregation.txt b/docs/topics/db/aggregation.txt index fbf3e51ebd..310745d869 100644 --- a/docs/topics/db/aggregation.txt +++ b/docs/topics/db/aggregation.txt @@ -193,24 +193,25 @@ Combining multiple aggregations with ``annotate()`` will `yield the wrong results <https://code.djangoproject.com/ticket/10060>`_ because joins are used instead of subqueries: - >>> Book.objects.first().authors.count() + >>> book = Book.objects.first() + >>> book.authors.count() 2 - >>> Book.objects.first().chapters.count() + >>> book.store_set.count() 3 - >>> q = Book.objects.annotate(Count('authors'), Count('chapters')) + >>> q = Book.objects.annotate(Count('authors'), Count('store')) >>> q[0].authors__count 6 - >>> q[0].chapters__count + >>> q[0].store__count 6 For most aggregates, there is no way to avoid this problem, however, the :class:`~django.db.models.Count` aggregate has a ``distinct`` parameter that may help: - >>> q = Book.objects.annotate(Count('authors', distinct=True), Count('chapters', distinct=True)) + >>> q = Book.objects.annotate(Count('authors', distinct=True), Count('store', distinct=True)) >>> q[0].authors__count 2 - >>> q[0].chapters__count + >>> q[0].store__count 3 .. admonition:: If in doubt, inspect the SQL query! |