Missing table alias in generated query after used in subquery

[Michal Čihař]

When running our tests against 4.0a1, it fails with:

 Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.9.7/x64/lib/python3.9/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
psycopg2.errors.UndefinedTable: missing FROM-clause entry for table "U0"
LINE 1: ...UNT(*) AS "__count" FROM "trans_component" WHERE ("U0"."repo...

It seems that the table alias is missing from the query. Full log can be seen at ​https://github.com/WeblateOrg/weblate/pull/6608/checks?check_run_id=3751233865

Reproducing outside the test case:

>>> from weblate.trans.models import Component
>>> from django.db.models import Q
>>> c = Component.objects.filter(Q(repo__in=('x', 'y')) | Q(repo__endswith='xxxx'))
>>> c.count()
0
>>> Component.objects.filter(linked_component__in=c).count()
0
>>> c.count()
Traceback (most recent call last):
  File "/home/nijel/weblate/weblate/.venv/lib/python3.9/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
psycopg2.errors.UndefinedTable: missing FROM-clause entry for table "U0"
LINE 1: ...UNT(*) AS "__count" FROM "trans_component" WHERE ("U0"."repo...
                                                             ^


The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/nijel/weblate/weblate/.venv/lib/python3.9/site-packages/django/db/models/query.py", line 416, in count
    return self.query.get_count(using=self.db)
  File "/home/nijel/weblate/weblate/.venv/lib/python3.9/site-packages/django/db/models/sql/query.py", line 515, in get_count
    number = obj.get_aggregation(using, ['__count'])['__count']
  File "/home/nijel/weblate/weblate/.venv/lib/python3.9/site-packages/django/db/models/sql/query.py", line 500, in get_aggregation
    result = compiler.execute_sql(SINGLE)
  File "/home/nijel/weblate/weblate/.venv/lib/python3.9/site-packages/django/db/models/sql/compiler.py", line 1198, in execute_sql
    cursor.execute(sql, params)
  File "/home/nijel/weblate/weblate/.venv/lib/python3.9/site-packages/django/db/backends/utils.py", line 98, in execute
    return super().execute(sql, params)
  File "/home/nijel/weblate/weblate/.venv/lib/python3.9/site-packages/django/db/backends/utils.py", line 66, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "/home/nijel/weblate/weblate/.venv/lib/python3.9/site-packages/django/db/backends/utils.py", line 75, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "/home/nijel/weblate/weblate/.venv/lib/python3.9/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "/home/nijel/weblate/weblate/.venv/lib/python3.9/site-packages/django/db/utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/home/nijel/weblate/weblate/.venv/lib/python3.9/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: missing FROM-clause entry for table "U0"
LINE 1: ...UNT(*) AS "__count" FROM "trans_component" WHERE ("U0"."repo...
                                                             ^

Note:

• The queryset has to consist of multiple Q
• Calling count on the queryset works until it is used in a subquery

[Mariusz Felisiak]

Thanks for the report!

Regression in e441847ecae99dd1ccd0d9ce76dbcff51afa863c, TBH I was pretty sure that this would introduce some regression, now we will have a proper regression test.

[Mariusz Felisiak]

​PR

[GitHub <noreply@…>]

In 903aaa3:

Fixed #33159 -- Reverted "Fixed #32970 -- Changed WhereNode.clone() to create a shallow copy of children."

This reverts commit e441847ecae99dd1ccd0d9ce76dbcff51afa863c.

A shallow copy is not enough because querysets can be reused and
evaluated in nested nodes, which shouldn't mutate JOIN aliases.

Thanks Michal Čihař for the report.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 93a42d43:

[4.0.x] Fixed #33159 -- Reverted "Fixed #32970 -- Changed WhereNode.clone() to create a shallow copy of children."

This reverts commit e441847ecae99dd1ccd0d9ce76dbcff51afa863c.

A shallow copy is not enough because querysets can be reused and
evaluated in nested nodes, which shouldn't mutate JOIN aliases.

Thanks Michal Čihař for the report.
Backport of 903aaa35e5ceaa33bfc9b19b7f6da65ce5a91dd4 from main