Fixed #23956 -- Fixed migration creation for multiple table inheritance

django/db/migrations/autodetector.py

@@ -463,7 +463,7 @@ class MigrationAutodetector(object):
                     if field.rel.to:
                         if field.primary_key:
                             primary_key_rel = field.rel.to
-                        else:
+                        elif not field.rel.parent_link:
                             related_fields[field.name] = field
                     # through will be none on M2Ms on swapped-out models;
                     # we can treat lack of through as auto_created=True, though.

docs/releases/1.7.2.txt

@@ -115,3 +115,7 @@ Bugfixes
 * Fixed index creation by the migration infrastructure, particularly when
   dealing with PostgreSQL specific {text|varchar}_pattern_ops indexes
   (:ticket:`23954`).
+
+* Fixed bug in ``makemigrations`` that created broken migration files when
+  dealing with multiple table inheritance and inheriting from more than one
+  model (:ticket:`23956`).

tests/migrations/test_autodetector.py

@@ -1446,6 +1446,29 @@ class AutodetectorTests(TestCase):
         self.assertOperationAttributes(changes, 'testapp', 0, 0, name="Author")
         self.assertOperationAttributes(changes, 'testapp', 0, 1, name="Aardvark")
 
+    def test_multiple_bases(self):
+        """#23956 - Tests that inheriting models doesn't move *_ptr fields into AddField operations."""
+        A = ModelState("app", "A", [("a_id", models.AutoField(primary_key=True))])
+        B = ModelState("app", "B", [("b_id", models.AutoField(primary_key=True))])
+        C = ModelState("app", "C", [], bases=("app.A", "app.B"))
+        D = ModelState("app", "D", [], bases=("app.A", "app.B"))
+        E = ModelState("app", "E", [], bases=("app.A", "app.B"))
+        # Make state
+        before = self.make_project_state([])
+        after = self.make_project_state([A, B, C, D, E])
+        autodetector = MigrationAutodetector(before, after)
+        changes = autodetector._detect_changes()
+        # Right number/type of migrations?
+        self.assertNumberMigrations(changes, "app", 1)
+        self.assertOperationTypes(changes, "app", 0, [
+            "CreateModel", "CreateModel", "CreateModel", "CreateModel", "CreateModel"
+        ])
+        self.assertOperationAttributes(changes, "app", 0, 0, name="A")
+        self.assertOperationAttributes(changes, "app", 0, 1, name="B")
+        self.assertOperationAttributes(changes, "app", 0, 2, name="C")
+        self.assertOperationAttributes(changes, "app", 0, 3, name="D")
+        self.assertOperationAttributes(changes, "app", 0, 4, name="E")
+
     def test_proxy_bases_first(self):
         """Tests that bases of proxies come first."""
         # Make state