Improve add_callback performance.

(imported from commit 4cea356ee6b0777bddfc996d7b8ee1b5fee391c6)

zephyr/models.py

@@ -53,8 +53,9 @@ class UserProfile(models.Model):
     def add_callback(self, cb, last_received):
         global callback_table
 
-        new_zephyrs = filter_by_subscriptions(
-                Zephyr.objects.filter(id__gt=last_received), self.user)
+        new_zephyrs = [um.message for um in
+                       UserMessage.objects.filter(user_profile=self,
+                                                  message__id__gt=last_received)]
 
         if new_zephyrs:
             return cb(new_zephyrs)