[1.9.x] Fixed #26413 -- Fixed a regression with abstract model inheritance and explicit parent links.

Thanks Trac alias trkjgrdg for the report and Tim for investigation and review.

Backport of 67cf5efa31acb2916034afb15610b700695dfcb0 from master

django/db/models/base.py

@@ -245,13 +245,21 @@ class ModelBase(type):
                     field = None
                 new_class._meta.parents[base] = field
             else:
+                base_parents = base._meta.parents.copy()
+
                 # .. and abstract ones.
                 for field in parent_fields:
                     new_field = copy.deepcopy(field)
                     new_class.add_to_class(field.name, new_field)
+                    # Replace parent links defined on this base by the new
+                    # field as it will be appropriately resolved if required.
+                    if field.one_to_one:
+                        for parent, parent_link in base_parents.items():
+                            if field == parent_link:
+                                base_parents[parent] = new_field
 
                 # Pass any non-abstract parent classes onto child.
-                new_class._meta.parents.update(base._meta.parents)
+                new_class._meta.parents.update(base_parents)
 
             # Inherit managers from the abstract base classes.
             new_class.copy_managers(base._meta.abstract_managers)

docs/releases/1.9.5.txt

@@ -40,3 +40,6 @@ Bugfixes
 
 * Restored the functionality of the admin's ``raw_id_fields`` in
   ``list_editable`` (:ticket:`26387`).
+
+* Fixed a regression with abstract model inheritance and explicit parent links
+  (:ticket:`26413`).

tests/model_inheritance/tests.py

@@ -2,9 +2,10 @@ from __future__ import unicode_literals
 
 from operator import attrgetter
 
+from django.apps.registry import Apps
 from django.core.exceptions import FieldError, ValidationError
 from django.core.management import call_command
-from django.db import connection
+from django.db import connection, models
 from django.test import TestCase, TransactionTestCase
 from django.test.utils import CaptureQueriesContext
 from django.utils import six
@@ -130,6 +131,26 @@ class ModelInheritanceTests(TestCase):
         m = MixinModel()
         self.assertEqual(m.other_attr, 1)
 
+    def test_abstract_parent_link(self):
+        test_apps = Apps(['model_inheritance'])
+
+        class A(models.Model):
+            class Meta:
+                apps = test_apps
+
+        class B(A):
+            a = models.OneToOneField('A', parent_link=True, on_delete=models.CASCADE)
+
+            class Meta:
+                apps = test_apps
+                abstract = True
+
+        class C(B):
+            class Meta:
+                apps = test_apps
+
+        self.assertIs(C._meta.parents[A], C._meta.get_field('a'))
+
 
 class ModelInheritanceDataTests(TestCase):
     @classmethod