docs: def update_count(self):
          """ updates rating count and rating average """
          node_rating_count = self.node.rating_count
          node_rating_count.rating_count = self.node.rating_set.count()
          node_rating_count.rating_avg = self.node.rating_set.aggregate(rate=Avg('value'))['rate']
  
          # if all ratings are deleted the value will be None!
          if node_rating_count.rating_avg is None:
              # set to 0 otherwise we'll get an exception
              node_rating_count.rating_avg = 0
  
          node_rating_count.save()