Re: [Django] #26491: Duplicated queries with nested prefetch

[Django]

#26491: Duplicated queries with nested prefetch
-+-
 Reporter:  duduklein|Owner:  nobody
 Type:   |   Status:  closed
  Cleanup/optimization   |
Component:  Database layer   |  Version:  1.9
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  duplicate
 Keywords:   | Triage Stage:
 |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by timgraham):

 * status:  new => closed
 * needs_better_patch:   => 0
 * needs_tests:   => 0
 * type:  Uncategorized => Cleanup/optimization
 * needs_docs:   => 0
 * resolution:   => duplicate


Comment:

 I tested the code from the description and this seems to be a duplicate of
 #25546 which is fixed in master (which will be Django 1.10).

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[Django] #26491: Duplicated queries with nested prefetch

[Django]

#26491: Duplicated queries with nested prefetch
--+
 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
--+
 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).

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Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

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