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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/ref/models/querysets.txt | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt index 71af4c5882..0ac8964e40 100644 --- a/docs/ref/models/querysets.txt +++ b/docs/ref/models/querysets.txt @@ -2977,6 +2977,14 @@ 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 |