Refs -- Updated docs about interaction between aggregations and QuerySet.order_by().
Obsolete since
@@ -505,15 +505,14 @@ include the aggregate column.
.. _aggregation-ordering-interaction:
-Interaction with default ordering or ``order_by()``
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Interaction with ``order_by()``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Fields that are mentioned in the ``order_by()`` part of a queryset (or which
-are used in the default ordering on a model) are used when selecting the
-output data, even if they are not otherwise specified in the ``values()``
-call. These extra fields are used to group "like" results together and they
-can make otherwise identical result rows appear to be separate. This shows up,
-particularly, when counting things.
+Fields that are mentioned in the ``order_by()`` part of a queryset are used
+when selecting the output data, even if they are not otherwise specified in the
+``values()`` call. These extra fields are used to group "like" results together
+and they can make otherwise identical result rows appear to be separate. This
+shows up, particularly, when counting things.
By way of example, suppose you have a model like this::
@@ -523,23 +522,20 @@ By way of example, suppose you have a model like this::
name = models.CharField(max_length=10)
data = models.IntegerField()
- class Meta:
- ordering = ["name"]
-
-The important part here is the default ordering on the ``name`` field. If you
-want to count how many times each distinct ``data`` value appears, you might
-try this::
+If you want to count how many times each distinct ``data`` value appears in an
+ordered queryset, you might try this::
+ items = Item.objects.order_by('name')
# Warning: not quite correct!
- Item.objects.values("data").annotate(Count("id"))
+ items.values('data').annotate(Count('id'))
...which will group the ``Item`` objects by their common ``data`` values and
then count the number of ``id`` values in each group. Except that it won't
-quite work. The default ordering by ``name`` will also play a part in the
-grouping, so this query will group by distinct ``(data, name)`` pairs, which
-isn't what you want. Instead, you should construct this queryset::
+quite work. The ordering by ``name`` will also play a part in the grouping, so
+this query will group by distinct ``(data, name)`` pairs, which isn't what you
+want. Instead, you should construct this queryset::
- Item.objects.values("data").annotate(Count("id")).order_by()
+ items.values('data').annotate(Count('id')).order_by()
...clearing any ordering in the query. You could also order by, say, ``data``
without any harmful effects, since that is already playing a role in the
