[1.6.x] Fixed #21787 -- regression in MTI .exclude() queries

Backpatch of 78a2617703bc1dada409f126db5c3db214913ff4 from master.

2 files changed, 24 insertions, 2 deletions

diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index 45276640e0..bb05c94e14 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -1256,6 +1256,7 @@ class Query(object):
         """
         path, names_with_path = [], []
         for pos, name in enumerate(names):
+            cur_names_with_path = (name, [])
             if name == 'pk':
                 name = opts.pk.name
             try:
@@ -1288,19 +1289,22 @@ class Query(object):
                         targets = (final_field.rel.get_related_field(),)
                         opts = int_model._meta
                         path.append(PathInfo(final_field.model._meta, opts, targets, final_field, False, True))
+                        cur_names_with_path[1].append(PathInfo(final_field.model._meta, opts, targets, final_field, False, True))
             if hasattr(field, 'get_path_info'):
                 pathinfos = field.get_path_info()
                 if not allow_many:
                     for inner_pos, p in enumerate(pathinfos):
                         if p.m2m:
-                            names_with_path.append((name, pathinfos[0:inner_pos + 1]))
+                            cur_names_with_path[1].extend(pathinfos[0:inner_pos + 1])
+                            names_with_path.append(cur_names_with_path)
                             raise MultiJoin(pos + 1, names_with_path)
                 last = pathinfos[-1]
                 path.extend(pathinfos)
                 final_field = last.join_field
                 opts = last.to_opts
                 targets = last.target_fields
-                names_with_path.append((name, pathinfos))
+                cur_names_with_path[1].extend(pathinfos)
+                names_with_path.append(cur_names_with_path)
             else:
                 # Local non-relational field.
                 final_field = field
diff --git a/tests/queries/tests.py b/tests/queries/tests.py
index ec708c6a51..6d59df6b0e 100644
--- a/tests/queries/tests.py
+++ b/tests/queries/tests.py
@@ -3008,3 +3008,21 @@ class Ticket21203Tests(TestCase):
         qs = Ticket21203Child.objects.select_related('parent').defer('parent__created')
         self.assertQuerysetEqual(qs, [c], lambda x: x)
         self.assertIs(qs[0].parent.parent_bool, True)
+
+
+class ForeignKeyToBaseExcludeTests(TestCase):
+    def test_ticket_21787(self):
+        sc1 = SpecialCategory.objects.create(special_name='sc1', name='sc1')
+        sc2 = SpecialCategory.objects.create(special_name='sc2', name='sc2')
+        sc3 = SpecialCategory.objects.create(special_name='sc3', name='sc3')
+        c1 = CategoryItem.objects.create(category=sc1)
+        CategoryItem.objects.create(category=sc2)
+        self.assertQuerysetEqual(
+            SpecialCategory.objects.exclude(
+                categoryitem__id=c1.pk).order_by('name'),
+            [sc2, sc3], lambda x: x
+        )
+        self.assertQuerysetEqual(
+            SpecialCategory.objects.filter(categoryitem__id=c1.pk),
+            [sc1], lambda x: x
+        )