'Limit the number of documents returned in a single batch (each
batch requires a round trip to the server).
See http://api.mongodb.com/python/current/api/pymongo/cursor.html#pymongo.cursor.Cursor.batch_size
for details.
:param size: desired size of each batch.'

def batch_size(self, size):

    queryset = self.clone()
    queryset._batch_size = size
    if queryset._cursor_obj:
        queryset._cursor_obj.batch_size(queryset._batch_size)
    return queryset
