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[2.2.x] Fixed #30325 -- Reverted "Fixed #29725 -- Removed unnecessary join in QuerySet.count() and exists() on a many-to-many relation."

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This reverts commit 1299421cad due to
a regression with custom managers.

Backport of 5f7991c42c from master
This commit is contained in:
Mariusz Felisiak
2019-04-15 10:35:37 +02:00
parent 86de106864
commit e8de1cc94c
4 changed files with 6 additions and 77 deletions
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27
django/db/models/fields/related_descriptors.py
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@@ -929,33 +929,6 @@ def create_forward_many_to_many_manager(superclass, rel, reverse):
False,
)
@property
def constrained_target(self):
# If the through relation's target field's foreign integrity is
# enforced, the query can be performed solely against the through
# table as the INNER JOIN'ing against target table is unnecessary.
if not self.target_field.db_constraint:
return None
db = router.db_for_read(self.through, instance=self.instance)
if not connections[db].features.supports_foreign_keys:
return None
hints = {'instance': self.instance}
manager = self.through._base_manager.db_manager(db, hints=hints)
filters = {self.source_field_name: self.instance.pk}
# Nullable target rows must be excluded as well as they would have
# been filtered out from an INNER JOIN.
if self.target_field.null:
filters['%s__isnull' % self.target_field_name] = False
return manager.filter(**filters)
def exists(self):
constrained_target = self.constrained_target
return constrained_target.exists() if constrained_target else super().exists()
def count(self):
constrained_target = self.constrained_target
return constrained_target.count() if constrained_target else super().count()
def add(self, *objs, through_defaults=None):
self._remove_prefetched_objects()
db = router.db_for_write(self.through, instance=self.instance)