code: def update_trackers(self):
          
          direct_approved_topics = self.topics.filter(approved=True).order_by('-last_post_on')
  
          # Compute the direct topics count and the direct posts count.
          self.direct_topics_count = direct_approved_topics.count()
          self.direct_posts_count = direct_approved_topics.aggregate(
              total_posts_count=Sum('posts_count'))['total_posts_count'] or 0
  
          # Forces the forum's 'last_post' ID and 'last_post_on' date to the corresponding values
          # associated with the topic with the latest post.
          if direct_approved_topics.exists():
              self.last_post_id = direct_approved_topics[0].last_post_id
              self.last_post_on = direct_approved_topics[0].last_post_on
          else:
              self.last_post_id = None
              self.last_post_on = None
  
          # Any save of a forum triggered from the update_tracker process will not result in checking
          # for a change of the forum's parent.
          self._simple_save()
docs: Updates the denormalized trackers associated with the forum instance.