[1.6.x] Fixed ._meta.pk_index() virtual field failure

Backport of 92476e880c from master

django/db/models/options.py

@@ -204,9 +204,10 @@ class Options(object):
 
     def pk_index(self):
         """
-        Returns the index of the primary key field in the self.fields list.
+        Returns the index of the primary key field in the self.concrete_fields
+        list.
         """
-        return self.fields.index(self.pk)
+        return self.concrete_fields.index(self.pk)
 
     def setup_proxy(self, target):
         """

tests/foreign_object/models.py

@@ -140,6 +140,9 @@ class Article(models.Model):
         except ArticleTranslation.DoesNotExist:
             return '[No translation found]'
 
+class NewsArticle(Article):
+    pass
+
 class ArticleTranslation(models.Model):
     article = models.ForeignKey(Article)
     lang = models.CharField(max_length='2')

tests/foreign_object/tests.py

@@ -1,7 +1,9 @@
 import datetime
 from operator import attrgetter
 
-from .models import Country, Person, Group, Membership, Friendship, Article, ArticleTranslation, ArticleTag, ArticleIdea
+from .models import (
+    Country, Person, Group, Membership, Friendship, Article,
+    ArticleTranslation, ArticleTag, ArticleIdea, NewsArticle)
 from django.test import TestCase
 from django.utils.translation import activate
 from django.core.exceptions import FieldError
@@ -339,6 +341,20 @@ class MultiColumnFKTests(TestCase):
         with self.assertRaises(FieldError):
             Article.objects.filter(ideas__name="idea1")
 
+    def test_inheritance(self):
+        activate("fi")
+        na = NewsArticle.objects.create(pub_date=datetime.date.today())
+        ArticleTranslation.objects.create(
+            article=na, lang="fi", title="foo", body="bar")
+        self.assertQuerysetEqual(
+            NewsArticle.objects.select_related('active_translation'),
+            [na], lambda x: x
+        )
+        with self.assertNumQueries(1):
+            self.assertEqual(
+                NewsArticle.objects.select_related(
+                    'active_translation')[0].active_translation.title,
+                "foo")
 
 class FormsTests(TestCase):
     # ForeignObjects should not have any form fields, currently the user needs