def update_counter_cache
      self.discussion.reply_count = Post.where(:discussion_id => self.discussion.id)
                                        .count - 1
      self.discussion.save
    end
def update_counter_cache
      self.discussion.reply_count = Post.where(:discussion_id => self.discussion.id)
                                        .count - 1
      self.discussion.save
    end
Custom counter cache.  Does not include the first post of a discussion.