#26491: Duplicated queries with nested prefetch
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Reporter: duduklein | Owner: nobody
Type: Uncategorized | Status: new
Component: Database layer (models, ORM) | Version: 1.9
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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This ticket may be related to #26318 , but it's not the same since it does
not involve repeated models.
Consider the following 3 test models:
{{{
class Test1(models.Model):
pass
class Test2(models.Model):
test1 = models.ForeignKey(Test1, related_name="tests2")
class Test3(models.Model):
test2 = models.ForeignKey(Test2, related_name="tests3")
}}}
Through the shell, we create initial entries and run the nested prefetch
queries. We verify that the last 2 queries are duplicated:
{{{
from test.models import Test1, Test2, test3
from django.db import connection
from django.db.models import Prefetch
t1 = Test1.objects.create()
t2 = Test2.objects.create(test1 = t1)
t3 = Test3.objects.create(test2 = t2)
connection.queries_log.clear()
tests2_prefetch = Prefetch("tests2",
Test2.objects.prefetch_related("tests3"))
Test1.objects.prefetch_related(tests2_prefetch)
assert len(connection.queries) == 4
assert connection.queries[-1] == connection.queries[-2]
}}}
We had 4 queries instead of 3 expected and the last 2 are duplicated (to
prefetch Test3 entries).
--
Ticket URL: <https://code.djangoproject.com/ticket/26491>
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