Fixed #26551 -- Fixed negated Q() queries that span relations.

Prevented queries from reusing trimmed joins.

tests/queries/models.py

@@ -648,8 +648,6 @@ class Employment(models.Model):
     title = models.CharField(max_length=128)
 
 
-# Bug #22429
-
 class School(models.Model):
     pass
 
@@ -659,6 +657,8 @@ class Student(models.Model):
 
 
 class Classroom(models.Model):
+    name = models.CharField(max_length=20)
+    has_blackboard = models.NullBooleanField()
     school = models.ForeignKey(School, models.CASCADE)
     students = models.ManyToManyField(Student, related_name='classroom')
 

tests/queries/tests.py

@@ -3147,6 +3147,25 @@ class JoinReuseTest(TestCase):
         qs = Author.objects.filter(report__name='r4').filter(report__name='r1')
         self.assertEqual(str(qs.query).count('JOIN'), 2)
 
+    def test_inverted_q_across_relations(self):
+        """
+        When a trimmable join is specified in the query (here school__), the
+        ORM detects it and removes unnecessary joins. The set of reusable joins
+        are updated after trimming the query so that other lookups don't
+        consider that the outer query's filters are in effect for the subquery
+        (#26551).
+        """
+        springfield_elementary = School.objects.create()
+        hogward = School.objects.create()
+        Student.objects.create(school=springfield_elementary)
+        hp = Student.objects.create(school=hogward)
+        Classroom.objects.create(school=hogward, name='Potion')
+        Classroom.objects.create(school=springfield_elementary, name='Main')
+        qs = Student.objects.filter(
+            ~(Q(school__classroom__name='Main') & Q(school__classroom__has_blackboard=None))
+        )
+        self.assertSequenceEqual(qs, [hp])
+
 
 class DisjunctionPromotionTests(TestCase):
     def test_disjunction_promotion_select_related(self):