filter on exists-subquery with empty queryset removes whole WHERE block

[Tobias Bengfort]

>>> qs = MyModel.objects.filter(~models.Exists(MyModel.objects.none()), name='test')
>>> qs
<QuerySet []>
>>> print(qs.query)
EmptyResultSet

With django-debug-toolbar I can still see the query, but there WHERE block is missing completely.

This seems to be very similar to #33018.

[Simon Charette]

I think that this is an issue with Exists.as_sql when self.invert is True.

Since Exists encapsulate its negation logic (see __invert__) it should catch EmptyResultSet when raised by its super() call in as_sql and return an always true predicate (e.g. 1=1).

Does the following patch address your issue?

django/db/models/expressions.py

@@ -1211 +1211 @@
 
     def as_sql(self, compiler, connection, template=None, **extra_context):
         query = self.query.exists(using=connection.alias)
-        sql, params = super().as_sql(
-            compiler,
-            connection,
-            template=template,
-            query=query,
-            **extra_context,
-        )
+        try:
+            sql, params = super().as_sql(
+                compiler,
+                connection,
+                template=template,
+                query=query,
+                **extra_context,
+            )
+        except EmptyResultSet:
+            if self.negated:
+                return '%s = %s', (1, 1)
+            raise
         if self.negated:
             sql = 'NOT {}'.format(sql)
         return sql, params

tests/expressions/tests.py

@@ -1905 +1905 @@
         )
         self.assertNotIn('ORDER BY', captured_sql)
 
+    def test_negated_empty_exists(self):
+        manager = Manager.objects.create()
+        qs = Manager.objects.filter(
+            ~Exists(Manager.objects.none()), pk=manager.pk
+        )
+        self.assertQuerysetEqual(qs, Manager.objects.filter(pk=manager.pk))
+
 
 class FieldTransformTests(TestCase):

[Mariusz Felisiak <felisiak.mariusz@…>]

In b7d1da5a:

Fixed #33482 -- Fixed QuerySet filtering againts negated Exists() with empty queryset.

Thanks Tobias Bengfort for the report.

[GitHub <noreply@…>]

In 6f185a5:

Refs #33482 -- Fixed QuerySet selecting and filtering againts negated Exists() with empty queryset.

Regression in b7d1da5a62fe4141beff2bfea565f7ef0038c94c.

[Tobias Bengfort]

I still get this error in 4.2 if I include the empty exists expression in the filter:

def test_filter_by_empty_exists(self):
    manager = Manager.objects.create()
    qs = Manager.objects.annotate(
        exists=Exists(Manager.objects.none())
    ).filter(pk=manager.pk, exists=False)
    self.assertSequenceEqual(qs, [manager])
    self.assertIs(qs.get().exists, False)

[Simon Charette]

The fact the problem manifests itself when the queryset is not negated was missed during the initial patch.

Tobias, can you confirm ​the following PR addresses the issue.

It seemed worth continuing the discussion here instead of creating a separate ticket.

[Tobias Bengfort]

Thanks for the quick response! It looks good. It fixed the bug in my application.

[GitHub <noreply@…>]

In ea596a52:

Refs #33482 -- Fixed QuerySet selecting and filtering againts Exists() with empty queryset.

Thanks Tobias Bengfort for the report.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 458bc9e:

[5.0.x] Refs #33482 -- Fixed QuerySet selecting and filtering againts Exists() with empty queryset.

Thanks Tobias Bengfort for the report.
Backport of ea596a52d9f905596cc5335930c8f2ac4511204c from main