[1.5.x] Fixed #19672 -- Error in negated Q() filtering

There was a variable overwrite error in negated join filtering. This
happened when add_filter() was adding the IS NULL condition to the
WHERE clause.

This is not a backport from master as there have been some other
refactorings which made this patch irrelevant.

The patch is from Ian Kelly.

django/db/models/sql/query.py

@@ -1193,15 +1193,15 @@ class Query(object):
             self.promote_joins(join_list)
             if lookup_type != 'isnull':
                 if len(join_list) > 1:
-                    for alias in join_list:
-                        if self.alias_map[alias].join_type == self.LOUTER:
-                            j_col = self.alias_map[alias].rhs_join_col
+                    for j_alias in join_list:
+                        if self.alias_map[j_alias].join_type == self.LOUTER:
+                            j_col = self.alias_map[j_alias].rhs_join_col
                             # The join promotion logic should never produce
                             # a LOUTER join for the base join - assert that.
                             assert j_col is not None
                             entry = self.where_class()
                             entry.add(
-                                (Constraint(alias, j_col, None), 'isnull', True),
+                                (Constraint(j_alias, j_col, None), 'isnull', True),
                                 AND
                             )
                             entry.negate()

tests/regressiontests/queries/models.py

@@ -64,6 +64,7 @@ class Annotation(models.Model):
 class ExtraInfo(models.Model):
     info = models.CharField(max_length=100)
     note = models.ForeignKey(Note)
+    value = models.IntegerField(null=True)
 
     class Meta:
         ordering = ['info']

tests/regressiontests/queries/tests.py

@@ -51,8 +51,8 @@ class Queries1Tests(BaseQuerysetTest):
 
         # Create these out of order so that sorting by 'id' will be different to sorting
         # by 'info'. Helps detect some problems later.
-        self.e2 = ExtraInfo.objects.create(info='e2', note=n2)
-        e1 = ExtraInfo.objects.create(info='e1', note=self.n1)
+        self.e2 = ExtraInfo.objects.create(info='e2', note=n2, value=41)
+        e1 = ExtraInfo.objects.create(info='e1', note=self.n1, value=42)
 
         self.a1 = Author.objects.create(name='a1', num=1001, extra=e1)
         self.a2 = Author.objects.create(name='a2', num=2002, extra=e1)
@@ -880,6 +880,14 @@ class Queries1Tests(BaseQuerysetTest):
             Item.objects.filter(Q(tags__name__in=['t4', 't3'])),
             [repr(i) for i in Item.objects.filter(~~Q(tags__name__in=['t4', 't3']))])
 
+    def test_ticket19672(self):
+        self.assertQuerysetEqual(
+            Report.objects.filter(Q(creator__isnull=False) &
+                                  ~Q(creator__extra__value=41)),
+            ['<Report: r1>']
+        )
+
+
 class Queries2Tests(TestCase):
     def setUp(self):
         Number.objects.create(num=4)