AttributeError when annotating with Exists(none()) and aggregation

[Matthijs Kooijman]

I ran into a problem with annotating a field with an Exists subquery, passing MyModel.objects.none() to Exists. On Django main branch, this throws an AttributeError, on 2.2.24 this returns an empty queryset (and printing the query attribute of the queryset raises EmptyResultSet).

Strangely enough this only seems to occur when I add a second annotation using an aggregation (I tried Sum, Max and Count). Adding a second aggregation using a plain field (e.g. F('id')) does not seem to trigger the problem. Each of the annotations individually also work, but not together.

It seems this already fails on the most basic (empty) model definition, no options or specific fields required.

I have not really investigated the details, I'm not too familiar with the query generating code.

Below is a testcase (ready to be included as a regression test).

--- a/tests/model_regress/tests.py
+++ b/tests/model_regress/tests.py
@@ -236,6 +236,18 @@ class Horse(models.Model, metaclass=HorseBase):
 
         self.assertEqual(Horse.horns, 1)
 
+    def test_exists_none_with_aggregate(self):
+        Party.objects.create()
+        qs = Party.objects.all().annotate(
+            foo=models.Count('id'),
+            bar=models.Exists(Party.objects.none()),
+        )
+        # Throws EmptyResultSet on 2.2.24, or AttributeError: 'NothingNode' object has no attribute
+        # 'get_source_expressions' on 3.2.6
+        qs.query
+        # Returns empty result on 2.2.24 or throws on 3.2.6
+        self.assertEqual(len(qs), 1)
+

./runtests.py model_regress.tests.ModelTests.test_exists_none_with_aggregate
(... snip some stuff ...)
Traceback (most recent call last):
  File "django/tests/model_regress/tests.py", line 249, in test_exists_empty_with_aggregate
    self.assertEqual(len(qs), 1)
  File "django/db/models/query.py", line 262, in __len__
    self._fetch_all()
  File "django/db/models/query.py", line 1352, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "django/db/models/query.py", line 51, in __iter__
    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
  File "django/db/models/sql/compiler.py", line 1185, in execute_sql
    sql, params = self.as_sql()
  File "django/db/models/sql/compiler.py", line 527, in as_sql
    extra_select, order_by, group_by = self.pre_sql_setup()
  File "django/db/models/sql/compiler.py", line 64, in pre_sql_setup
    group_by = self.get_group_by(self.select + extra_select, order_by)
  File "django/db/models/sql/compiler.py", line 129, in get_group_by
    cols = expr.get_group_by_cols()
  File "django/db/models/expressions.py", line 1159, in get_group_by_cols
    external_cols = self.get_external_cols()
  File "django/db/models/expressions.py", line 1143, in get_external_cols
    return self.query.get_external_cols()
  File "django/db/models/sql/query.py", line 1057, in get_external_cols
    return [
  File "django/db/models/sql/query.py", line 1057, in <listcomp>
    return [
  File "django/db/models/sql/query.py", line 1697, in _gen_cols
    expr.get_source_expressions(),
AttributeError: 'NothingNode' object has no attribute 'get_source_expressions'

(Can be pulled from ​https://github.com/matthijskooijman/django/blob/testcase-exists-none/tests/model_regress/tests.py#L239)

[Mariusz Felisiak]

Thanks for the report. It's really similar to the #33018, however ​the proposed patch doesn't fix this issue.

[David Wobrock]

Hi,

Indeed, the bug seems close to #33018 but their scopes differ in my opinion.

From a quick bisect, it would seem that this regression has been introduced in #31094 and more precisely this commit ​https://github.com/django/django/pull/12227/commits/5a4d7285bd10bd40d9f7e574a7c421eb21094858

I'll try to have a look and submit a patch.

[David Wobrock]

Submitted a PR, with a tiny diff :)

See ​https://github.com/django/django/pull/14818

[Mariusz Felisiak]

Yes it is regression in 5a4d7285bd10bd40d9f7e574a7c421eb21094858.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 691486a5:

Fixed #33073 -- Fixed queryset crash with aggregation and empty/extra queryset annotation.

[Matthijs Kooijman]

Thanks for the superquick fix. I can't quickly test it on my original problem (my project is still stuck on 2.x, really need to upgrade soon), but I'll try to remember to do so once I've upgraded :-)