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Code Issues 25 Releases Wiki Activity

Fixed #27193 -- Preserved ordering in select_for_update subqueries.

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This commit is contained in:
François Freitag 2016-09-28 22:39:50 -07:00 committed by Tim Graham
parent 9e26a8331d
commit 8ac115c730
2 changed files with 14 additions and 2 deletions
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7
django/db/models/sql/compiler.py
View File

@ -476,8 +476,11 @@ class SQLCompiler(object):
Used when nesting this query inside another.
"""
obj = self.query.clone()
if obj.low_mark == 0 and obj.high_mark is None and not self.query.distinct_fields:
# If there is no slicing in use, then we can safely drop all ordering
# It's safe to drop ordering if the queryset isn't using slicing,
# distinct(*fields) or select_for_update().
if (obj.low_mark == 0 and obj.high_mark is None and
not self.query.distinct_fields and
not self.query.select_for_update):
obj.clear_ordering(True)
nested_sql = obj.get_compiler(connection=self.connection).as_sql(subquery=True)
if nested_sql == ('', ()):

9
tests/select_for_update/tests.py
View File

@ -300,3 +300,12 @@ class SelectForUpdateTests(TransactionTestCase):
def test_nowait_and_skip_locked(self):
with self.assertRaisesMessage(ValueError, 'The nowait option cannot be used with skip_locked.'):
Person.objects.select_for_update(nowait=True, skip_locked=True)
def test_ordered_select_for_update(self):
"""
Subqueries should respect ordering as an ORDER BY clause may be useful
to specify a row locking order to prevent deadlocks (#27193).
"""
with transaction.atomic():
qs = Person.objects.filter(id__in=Person.objects.order_by('-id').select_for_update())
self.assertIn('ORDER BY', str(qs.query))