Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  François
 |  Freitag
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Release blocker  |   Resolution:  fixed
 Keywords:  prefetch | Triage Stage:  Ready for
  AttributeError prefetch_related|  checkin
  nested RelatedManager  |
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Tim Graham ):

 In [changeset:"c679ac04499798e366ca594f97e4f95d3da3682f" c679ac04]:
 {{{
 #!CommitTicketReference repository=""
 revision="c679ac04499798e366ca594f97e4f95d3da3682f"
 [1.11.x] Fixed #27554 -- Fixed prefetch_related() crash when fetching
 relations in nested Prefetches.

 Backport of c0a2b9508aa2c6eaa22e9787010276edca887f0b from master
 }}}

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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  François
 |  Freitag
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Release blocker  |   Resolution:  fixed
 Keywords:  prefetch | Triage Stage:  Ready for
  AttributeError prefetch_related|  checkin
  nested RelatedManager  |
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Tim Graham ):

 * status:  assigned => closed
 * resolution:   => fixed


Comment:

 In [changeset:"c0a2b9508aa2c6eaa22e9787010276edca887f0b" c0a2b950]:
 {{{
 #!CommitTicketReference repository=""
 revision="c0a2b9508aa2c6eaa22e9787010276edca887f0b"
 Fixed #27554 -- Fixed prefetch_related() crash when fetching relations in
 nested Prefetches.
 }}}

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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  François
 |  Freitag
 Type:  Bug  |   Status:  assigned
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Release blocker  |   Resolution:
 Keywords:  prefetch | Triage Stage:  Ready for
  AttributeError prefetch_related|  checkin
  nested RelatedManager  |
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Tim Graham):

 * severity:  Normal => Release blocker
 * stage:  Accepted => Ready for checkin


Comment:

 The ticket wasn't tagged as a regression (release blocker) so
 unfortunately we missed the time to incorporate the fix in 1.10 which is
 now receiving only security updates. I'll backport the fix to 1.11.

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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  François
 |  Freitag
 Type:  Bug  |   Status:  assigned
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  prefetch | Triage Stage:  Accepted
  AttributeError prefetch_related|
  nested RelatedManager  |
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Pascal Briet):

 Any update on this issue ?
 It prevents us from migrating to 1.10

 Thanks !

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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  François
 |  Freitag
 Type:  Bug  |   Status:  assigned
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  prefetch | Triage Stage:  Accepted
  AttributeError prefetch_related|
  nested RelatedManager  |
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by François Freitag):

 * owner:  nobody => François Freitag
 * status:  new => assigned
 * has_patch:  0 => 1


Comment:

 [https://github.com/django/django/pull/8143 PR]

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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  prefetch | Triage Stage:  Accepted
  AttributeError prefetch_related|
  nested RelatedManager  |
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Simon Charette):

 #27744 was a duplicate.

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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  prefetch | Triage Stage:  Accepted
  AttributeError prefetch_related|
  nested RelatedManager  |
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by François Freitag):

 * cc: mail@… (added)


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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  prefetch | Triage Stage:  Accepted
  AttributeError prefetch_related|
  nested RelatedManager  |
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by vimarshc):

 Hey,

 Just finished "bisecting the exact commit which introduced the
 regression".
 Posting my results here.

 Git output:
 {{{
 bdbe50a491ca41e7d4ebace47bfe8abe50a58211 is the first bad commit
 commit bdbe50a491ca41e7d4ebace47bfe8abe50a58211
 Author: François Freitag 
 Date:   Sun Jan 10 17:54:57 2016 +0100

 Fixed #25546 -- Prevented duplicate queries with nested
 prefetch_related().

 :04 04 5ad2af54d2f98566bbfdc23e04493e4c98262568
 f3488a5f680bc5d4b18249aed299b6abd5f86de9 M  django
 :04 04 59faff56062b7a347956e24315e12beeb5c7d704
 c4a686067f06b7056dafffa1013bfe3c018c5e52 M  tests
 bisect run success

 }}}

 I'll start trying to locate and fix the bug. I'll request the bug be
 assigned to me once I'm confident I can resolve the issue.
 I'm attaching a directory with the models and tests inside it.
 This directory was inside the tests directory.
 I've written three test cases out of which 2 are passing and one is
 failing. (the one that is failing is
 "test_case_for_nested_and_flat_prefetches")

 [https://github.com/vimarshc/django Here] is a link to the django repo I
 forked and I've pushed the aforementioned tests here too if someone wants
 to get them from here.
 They're on the nested-bug-1.10 branch.

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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  prefetch | Triage Stage:  Accepted
  AttributeError prefetch_related|
  nested RelatedManager  |
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by vimarshc):

 * Attachment "flattened-prefetch.zip" added.

 test cases for bug

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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  prefetch | Triage Stage:  Accepted
  AttributeError prefetch_related|
  nested RelatedManager  |
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Vimarsh Chaturvedi):

 Hey guys,

 My first time posting here.

 I tried reproducing the bug, and was able to.
 I added the following cases as per Simon Charette's suggestion and Django
 didn't throw any exception.

 views.py
 {{{
 #Code in orinigal test project by Anthony Leontiev
 def setup():
 a = A.objects.create()
 b = B.objects.create()

 b.a = a
 b.save()

 d = D.objects.create()
 C.objects.create(b=b, d=d)


 #Succeeded: As reported above.
 def nested_prefetch(request, *args, **kwargs):
 setup()
 queryset = A.objects.all().prefetch_related(
 Prefetch(
 'b',
 queryset=B.objects.all().prefetch_related(
 Prefetch(
 'c',
 queryset=C.objects.all().prefetch_related(
 'd'
 )
 )
 )
 )
 )
 content = queryset[0].b.c.all()[0].d.pk
 return HttpResponse(content)

 #Failed: As reported above.
 def flat_prefetch(request, *args, **kwargs):
 setup()
 queryset = A.objects.all().prefetch_related(
 Prefetch(
 'b',
 queryset=B.objects.all().prefetch_related(
 Prefetch('c__d')
 )
 )
 )
 content = queryset[0].b.c.all()[0].d.pk
 return HttpResponse(content)

 #The following three cases were added by me
 #Failed: As expected.
 def flat_prefetch_one(request, *args, **kwargs):
 setup()
 queryset = A.objects.all().prefetch_related(
 Prefetch(
 'b',
 queryset=B.objects.all().prefetch_related('c__d')
 )
 )
 content = queryset[0].b.c.all()[0].d.pk
 return HttpResponse(content)

 #Succeeded: I  was expecting this and the following case to fail too, but
 they didn't.
 def flat_prefetch_two(request, *args, **kwargs):
 setup()
 queryset = A.objects.all().prefetch_related(
 Prefetch('b__c__d')
 )
 content = queryset[0].b.c.all()[0].d.pk
 return HttpResponse(content)

 #succeeded
 def flat_prefetch_three(request, *args, **kwargs):
 setup()
 queryset = A.objects.all().prefetch_related('b__c__d')
 content = queryset[0].b.c.all()[0].d.pk
 return HttpResponse(content)
 }}}

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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  prefetch | Triage Stage:  Accepted
  AttributeError prefetch_related|
  nested RelatedManager  |
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Simon Charette):

 * stage:  Unreviewed => Accepted


Comment:

 I haven't tried reproducing myself but the report is complete enough that
 I trust the developer's judgment.

 Anthony, can you confirm this is also an issue when running
 `A.objects.prefetch_related('b__c__d'')`? What about
 `B.objects.prefetch_related('c__d')`?

 [https://docs.djangoproject.com/en/1.10/internals/contributing/triaging-
 tickets/#bisecting-a-regression Bisecting the exact commit that introduced
 the regression] would also be useful.

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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  prefetch | Triage Stage:
  AttributeError prefetch_related|  Unreviewed
  nested RelatedManager  |
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Anthony Leontiev):

 Discovered in an API integration test that relies on nested prefetching
 during an upgrade of Django 1.7 to Django 1.10.

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Re: [Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
 Reporter:  Anthony Leontiev |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.10
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  prefetch | Triage Stage:
  AttributeError prefetch_related|  Unreviewed
  nested RelatedManager  |
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Anthony Leontiev):

 * Attachment "prefetchbug.tar.gz" added.

 test project to reproduce the bug

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[Django] #27554: Queryset evaluation fails with mix of nested and flattened prefetches (AttributeError on RelatedManager)

[Django]

#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-+-
   Reporter:  Anthony|  Owner:  nobody
  Leontiev   |
   Type:  Bug| Status:  new
  Component:  Database   |Version:  1.10
  layer (models, ORM)|   Keywords:  prefetch
   Severity:  Normal |  AttributeError prefetch_related
   Triage Stage: |  nested RelatedManager
  Unreviewed |  Has patch:  0
Needs documentation:  0  |Needs tests:  0
Patch needs improvement:  0  |  Easy pickings:  0
  UI/UX:  0  |
-+-
 Under certain circumstances, querysets with nested prefetches fail to
 evaluate in Django 1.10.

 With these models (populated with data):

 {{{
 #  A <-> B <-- C --> D
 #\__/


 class A(models.Model):
 pass


 class B(models.Model):
 a = models.OneToOneField('A', null=True, related_name='b')
 d = models.ManyToManyField('D', through='C', related_name='b')


 class C(models.Model):
 b = models.ForeignKey('B', related_name='c')
 d = models.ForeignKey('D', related_name='c')


 class D(models.Model):
 pass
 }}}

 ... and this query/evaluation:

 {{{
 queryset = A.objects.all().prefetch_related(
 Prefetch(
 'b',
 queryset=B.objects.all().prefetch_related(
 Prefetch('c__d')
 )
 )
 )
 content = queryset[0].b.c.all()[0].d.pk
 }}}

 Django throws this exception:

 {{{
   File "/Users/ant/code/django-bugs/prefetchbug/.venv/lib/python2.7/site-
 packages/django/db/models/query.py", line 256, in __iter__
 self._fetch_all()
   File "/Users/ant/code/django-bugs/prefetchbug/.venv/lib/python2.7/site-
 packages/django/db/models/query.py", line 1087, in _fetch_all
 self._prefetch_related_objects()
   File "/Users/ant/code/django-bugs/prefetchbug/.venv/lib/python2.7/site-
 packages/django/db/models/query.py", line 663, in
 _prefetch_related_objects
 prefetch_related_objects(self._result_cache,
 *self._prefetch_related_lookups)
   File "/Users/ant/code/django-bugs/prefetchbug/.venv/lib/python2.7/site-
 packages/django/db/models/query.py", line 1460, in
 prefetch_related_objects
 (through_attr, first_obj.__class__.__name__, lookup.prefetch_through))
 AttributeError: Cannot find 'd' on RelatedManager object, 'b__c__d' is an
 invalid parameter to prefetch_related()
 }}}

 Interestingly enough, this practically identical variant of the above
 query with a fully "nested" prefetch structure succeeds:

 {{{
 queryset = A.objects.all().prefetch_related(
 Prefetch(
 'b',
 queryset=B.objects.all().prefetch_related(
 Prefetch(
 'c',
 queryset=C.objects.all().prefetch_related(
 'd'
 )
 )
 )
 )
 )
 content = queryset[0].b.c.all()[0].d.pk
 }}}


 To reproduce, download the attachment and run:

 {{{
 pip install -r requirements.txt
 python manage.py migrate
 python manage.py runserver
 }}}

 ... and navigate to {localhost:8000/flat} and {localhost:8000/nested}.

 This only seems to impact Django 1.10; the bug does not reproduce if the
 Django version in the {requirements.txt} file is changed to 1.9 or 1.8.

 Discovered in https://github.com/AltSchool/dynamic-rest/pull/147
 Similar to https://code.djangoproject.com/ticket/26801

--
Ticket URL: 
Django 
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