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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def update_trackers(self):
 """ Updates the denormalized trackers associated with the topic instance. """

        self.posts_count = self.posts.filter(approved=True).count()
        first_post = self.posts.all().order_by('created').first()
        last_post = self.posts.filter(approved=True).order_by('-created').first()
        self.first_post = first_post
        self.last_post = last_post
        self.last_post_on = last_post.created if last_post else None
        self._simple_save()
        # Trigger the forum-level trackers update
        self.forum.update_trackers()