#26959: AssertionError in query.py change_aliases
----------------------------------------------+--------------------
     Reporter:  brownan                       |      Owner:  nobody
         Type:  Bug                           |     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
----------------------------------------------+--------------------
 I'm running into this AssertionError on a fairly complex query in my app,
 involving ORing two querysets together.

 I've tried on both Django 1.9.8 and 1.10rc1

 Here's the backtrace:
 {{{
 Traceback (most recent call last):
   File "/.../app/tests.py", line 32, in test_asserterror
     return qs1 | qs2
   File "/.../env/local/lib/python2.7/site-
 packages/django/db/models/query.py", line 318, in __or__
     combined.query.combine(other.query, sql.OR)
   File "/.../env/local/lib/python2.7/site-
 packages/django/db/models/sql/query.py", line 573, in combine
     w.relabel_aliases(change_map)
   File "/.../env/local/lib/python2.7/site-
 packages/django/db/models/sql/where.py", line 129, in relabel_aliases
     child.relabel_aliases(change_map)
   File "/.../env/local/lib/python2.7/site-
 packages/django/db/models/sql/where.py", line 131, in relabel_aliases
     self.children[pos] = child.relabeled_clone(change_map)
   File "/.../env/local/lib/python2.7/site-
 packages/django/db/models/lookups.py", line 103, in relabeled_clone
     new.rhs = new.rhs.relabeled_clone(relabels)
   File "/.../env/local/lib/python2.7/site-
 packages/django/db/models/sql/query.py", line 346, in relabeled_clone
     clone.change_aliases(change_map)
   File "/.../env/local/lib/python2.7/site-
 packages/django/db/models/sql/query.py", line 793, in change_aliases
     assert set(change_map.keys()).intersection(set(change_map.values()))
 == set()
 AssertionError
 }}}

 And I've managed to simplify down a test case the best I could.

 models.py:

 {{{#!python
 class Group(models.Model):
     pass

 class User(models.Model):
     groups = models.ManyToManyField(Group, related_name="members_of")
     friends = models.ManyToManyField('self')
 }}}

 test case:
 {{{#!python
 g1 = models.Group.objects.create()
 g2 = models.Group.objects.create()
 g3 = models.Group.objects.create()

 u1 = models.User.objects.create()

 otherusers = models.User.objects.exclude(
     pk=u1.pk
 ).exclude(
     friends=u1
 )

 qs1 = otherusers.filter(
     groups=g1
 ).filter(
     groups=g2
 )

 qs2 = otherusers.filter(
     groups=g1
 ).filter(
     groups=g3
 )

 qs1 | qs2
 }}}

 Let me know if I can provide any other information that would  be helpful.
 Oddly enough in my app it only happens part of the time, seemingly at
 random, but this test case seems to hit the assertion every time for me.

--
Ticket URL: <https://code.djangoproject.com/ticket/26959>
Django <https://code.djangoproject.com/>
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