bulk_update: Do updates in bulk where applicable.

zerver/lib/bulk_create.py

@@ -90,14 +90,14 @@ def bulk_set_users_or_streams_recipient_fields(model: Model,
 
     objects_dict = {obj.id: obj for obj in objects}
 
+    objects_to_update = set()
     for recipient in recipients:
         assert recipient.type == recipient_type
         result = objects_dict.get(recipient.type_id)
         if result is not None:
             result.recipient = recipient
-            # TODO: Django 2.2 has a bulk_update method, so once we manage to migrate to that version,
-            # we take adventage of this, instead of calling save individually.
-            result.save(update_fields=['recipient'])
+            objects_to_update.add(result)
+    model.objects.bulk_update(objects_to_update, ['recipient'])
 
 # This is only sed in populate_db, so doesn't really need tests
 def bulk_create_streams(realm: Realm,

zerver/management/commands/deliver_scheduled_messages.py

@@ -65,7 +65,7 @@ Usage: ./manage.py deliver_scheduled_messages
                     with transaction.atomic():
                         do_send_messages([self.construct_message(message)])
                         message.delivered = True
-                        message.save(update_fields=['delivered'])
+                Message.objects.bulk_update(messages_to_deliver, ['delivered'])
 
             cur_time = timezone_now()
             time_next_min = (cur_time + timedelta(minutes=1)).replace(second=0, microsecond=0)