From be1b776ad8d6f9bccfbdf63f84b16fb81a13119e Mon Sep 17 00:00:00 2001 From: Babak Mahmoudy Date: Tue, 1 Apr 2025 19:34:59 +1100 Subject: [PATCH] Fixed #36213 -- Doc'd MySQL's handling of self-select updates in QuerySet.update(). Co-authored-by: Andro Ranogajec --- docs/ref/models/querysets.txt | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt index e16d6668ee..c7e8b974a7 100644 --- a/docs/ref/models/querysets.txt +++ b/docs/ref/models/querysets.txt @@ -2961,6 +2961,14 @@ Using ``update()`` also prevents a race condition wherein something might change in your database in the short period of time between loading the object and calling ``save()``. +.. admonition:: MySQL does not support self-select updates + + On MySQL, ``QuerySet.update()`` may execute a ``SELECT`` followed by an + ``UPDATE`` instead of a single ``UPDATE`` when filtering on related tables, + which can introduce a race condition if concurrent changes occur between + the queries. To ensure atomicity, consider using transactions or avoiding + such filter conditions on MySQL. + Finally, realize that ``update()`` does an update at the SQL level and, thus, does not call any ``save()`` methods on your models, nor does it emit the :attr:`~django.db.models.signals.pre_save` or