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Diffstat (limited to 'docs/ref')
| -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 fe2c827e63..bd20fbdcea 100644 --- a/docs/ref/models/querysets.txt +++ b/docs/ref/models/querysets.txt @@ -1628,6 +1628,19 @@ specify the related objects you want to lock in ``select_for_update(of=(...))`` using the same fields syntax as :meth:`select_related`. Use the value ``'self'`` to refer to the queryset's model. +You can't use ``select_for_update()`` on nullable relations:: + + >>> Person.objects.select_related('hometown').select_for_update() + Traceback (most recent call last): + ... + django.db.utils.NotSupportedError: FOR UPDATE cannot be applied to the nullable side of an outer join + +To avoid that restriction, you can exclude null objects if you don't care about +them:: + + >>> Person.objects.select_related('hometown').select_for_update().exclude(hometown=None) + <QuerySet [<Person: ...)>, ...]> + Currently, the ``postgresql``, ``oracle``, and ``mysql`` database backends support ``select_for_update()``. However, MySQL doesn't support the ``nowait``, ``skip_locked``, and ``of`` arguments. |