Fixed #7181 -- when ordering by a potentially NULL field, use a left-outer join

so that the ordering doesn't accidentally restrict the result set.

(Ironically, one existing test actually showed this problem, but I was too
dumb to notice the result was incorrect.)


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7761 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/sql/query.py

@@ -610,6 +610,10 @@ class Query(object):
         alias = joins[-1]
         col = target.column
 
+        # Must use left outer joins for nullable fields.
+        for join in joins:
+            self.promote_alias(join)
+
         # If we get to this point and the field is a relation to another model,
         # append the default ordering for that model.
         if field.rel and len(joins) > 1 and opts.ordering: