From e124d2da94cc1233729d8f0200809589f6c5afc8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fran=C3=A7ois=20Freitag?= <mail@franek.fr>
Date: Wed, 26 Oct 2016 18:01:37 -0400
Subject: [PATCH] Fixed #26551 -- Fixed negated Q() queries that span
 relations.

Prevented queries from reusing trimmed joins.
---
 AUTHORS                       |  1 +
 django/db/models/sql/query.py |  6 ++++--
 tests/queries/models.py       |  4 ++--
 tests/queries/tests.py        | 19 +++++++++++++++++++
 4 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/AUTHORS b/AUTHORS
index 984b49f4f5..e67a9014d1 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -258,6 +258,7 @@ answer newbie questions, and generally made Django that much better:
     flavio.curella@gmail.com
     Florian Apolloner <florian@apolloner.eu>
     Francisco Albarran Cristobal <pahko.xd@gmail.com>
+    François Freitag <mail@franek.fr>
     Frank Tegtmeyer <fte@fte.to>
     Frank Wierzbicki
     Frank Wiles <frank@revsys.com>
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index f76519401b..9040c5a5a4 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -1192,10 +1192,12 @@ class Query:
             return self.split_exclude(filter_expr, LOOKUP_SEP.join(parts[:e.level]),
                                       can_reuse, e.names_with_path)
 
-        if can_reuse is not None:
-            can_reuse.update(join_list)
+        # Update used_joins before trimming since they are reused to determine
+        # which joins could be later promoted to INNER.
         used_joins = set(used_joins).union(set(join_list))
         targets, alias, join_list = self.trim_joins(sources, join_list, path)
+        if can_reuse is not None:
+            can_reuse.update(join_list)
 
         if field.is_relation:
             # No support for transforms for relational fields
diff --git a/tests/queries/models.py b/tests/queries/models.py
index 592359c796..25fd673272 100644
--- a/tests/queries/models.py
+++ b/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')
 
diff --git a/tests/queries/tests.py b/tests/queries/tests.py
index d6e726d4d3..c4181a10b5 100644
--- a/tests/queries/tests.py
+++ b/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):