[1.7.x] Fixed #19195 -- Allow explicit ordering by a relation `_id` field.

Thanks to chrisedgemon for the report and shaib, akaariai and
timgraham for the review.

Backport of 24ec9538b7 from master

1 files changed, 5 insertions, 11 deletions

diff --git a/tests/ordering/models.py b/tests/ordering/models.py
index 415b28bb41..2ab16f3c5f 100644
--- a/tests/ordering/models.py
+++ b/tests/ordering/models.py
@@ -17,25 +17,19 @@ from django.db import models
 from django.utils.encoding import python_2_unicode_compatible
 
 
-@python_2_unicode_compatible
-class Article(models.Model):
-    headline = models.CharField(max_length=100)
-    pub_date = models.DateTimeField()
-
+class Author(models.Model):
     class Meta:
-        ordering = ('-pub_date', 'headline')
-
-    def __str__(self):
-        return self.headline
+        ordering = ('-pk',)
 
 
 @python_2_unicode_compatible
-class ArticlePKOrdering(models.Model):
+class Article(models.Model):
+    author = models.ForeignKey(Author, null=True)
     headline = models.CharField(max_length=100)
     pub_date = models.DateTimeField()
 
     class Meta:
-        ordering = ('-pk',)
+        ordering = ('-pub_date', 'headline')
 
     def __str__(self):
         return self.headline