Fixed #5420 -- Added support for delayed loading of model fields.

In extreme cases, some fields are expensive to load from the database
(e.g. GIS fields requiring conversion, or large text fields). This
commit adds defer() and only() methods to querysets that allow the
caller to specify which fields should not be loaded unless they are
accessed.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10090 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/options.py

@@ -477,3 +477,9 @@ class Options(object):
             self._ordered_objects = objects
         return self._ordered_objects
 
+    def pk_index(self):
+        """
+        Returns the index of the primary key field in the self.fields list.
+        """
+        return self.fields.index(self.pk)
+