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Fixed #29499 -- Fixed race condition in QuerySet.update_or_create().

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A race condition happened when the object didn't already exist and
another process/thread created the object before update_or_create()
did and then attempted to update the object, also before update_or_create()
saved the object. The update by the other process/thread could be lost.
This commit is contained in:
Michael Sanders 2018-08-01 10:52:28 +01:00 • committed by Tim Graham
parent 743d28f553
commit 271542dad1
8 changed files with 96 additions and 5 deletions
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9
django/db/models/query.py
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@ -501,7 +501,9 @@ class QuerySet:
obj = self.select_for_update().get(**kwargs)
except self.model.DoesNotExist:
params = self._extract_model_params(defaults, **kwargs)
obj, created = self._create_object_from_params(kwargs, params)
# Lock the row so that a concurrent update is blocked until
# after update_or_create() has performed its save.
obj, created = self._create_object_from_params(kwargs, params, lock=True)
if created:
return obj, created
for k, v in defaults.items():
@ -509,7 +511,7 @@ class QuerySet:
obj.save(using=self.db)
return obj, False
def _create_object_from_params(self, lookup, params):
def _create_object_from_params(self, lookup, params, lock=False):
"""
Try to create an object using passed params. Used by get_or_create()
and update_or_create().
@ -521,7 +523,8 @@ class QuerySet:
return obj, True
except IntegrityError as e:
try:
return self.get(**lookup), False
qs = self.select_for_update() if lock else self
return qs.get(**lookup), False
except self.model.DoesNotExist:
pass
raise e