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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/ref/models/querysets.txt | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt index fc1c5571e0..99feac4318 100644 --- a/docs/ref/models/querysets.txt +++ b/docs/ref/models/querysets.txt @@ -1211,6 +1211,19 @@ results; these ``QuerySets`` are then used in the ``self.toppings.all()`` calls. The additional queries in ``prefetch_related()`` are executed after the ``QuerySet`` has begun to be evaluated and the primary query has been executed. +Note that there is no mechanism to prevent another database query from altering +the items in between the execution of the primary query and the additional +queries, which could produce an inconsistent result. For example, if a +``Pizza`` is deleted after the primary query has executed, its toppings will +not be returned in the additional query, and it will seem like the pizza has no +toppings: + +.. code-block:: pycon + + >>> Pizza.objects.prefetch_related("toppings") + # "Hawaiian" Pizza was deleted in another shell. + <QuerySet [<Pizza: Hawaiian ()>, <Pizza: Seafood (prawns, smoked salmon)>]> + If you have an iterable of model instances, you can prefetch related attributes on those instances using the :func:`~django.db.models.prefetch_related_objects` function. |