public function get_actual_last_post()
    {
      $cid = 'lastpost_forum_' . $this->data['fid'];

      if(cache::exists($cid))
    {
      return cache::get($cid);
    }

    // now get the last post for this forum
    $lastpost = db::prepexec('SELECT MAX(p.pid) pid, t.tid, d.did
        FROM post p
        JOIN discussion d ON (p.discussion = d.did)
        JOIN thread t ON (t.discussion = d.did)
        WHERE t.forum = ?
        AND p.deleted = 0
        AND t.deleted = 0
        GROUP BY tid, did
        ORDER BY pid DESC
        LIMIT 1',
        array(
          $this->data['fid']
          )
        )->fetch();

    if(!$lastpost)
    {
      $lastpost = null;
    }
    cache::set($cid, $lastpost);

    return $lastpost;
    }

    // A test function to get the last post in a different way
    public function get_last_post(user $user)
    {
    // if the user can not see all posts, then we don't want to show a last
    // post.
    if(!allowed::userCanSeeAllPosts($this, $user))
    {
      return null;
    }

    // get all direct children
    $tree = self::getTree(self::getAll());
    $forumid = $this->data['fid'];
    $subforums = array();
    $lastposts = array();
    if(array_key_exists($forumid, $tree))
    {
        $subforums = $tree[ $forumid ];
        foreach($subforums as $subforum)
        {
            $forum = forum::fromId( $subforum );
            if($forum !== null)
            {
                $lp = $forum->get_last_post($user);
                if($lp !== null)
                {
                    $lastposts[] = $lp;
                }
            }
        }
    }

    $lastpost = $this->get_actual_last_post();

    if($lastpost !== null)
    {
        $lastposts[] = $lastpost;
    }

    $highest = null;
    if($lastposts)
    {
        foreach($lastposts as $lastpost)
        {
            if((!$highest) || $highest['pid'] < $lastpost['pid'])
            {
                $highest = $lastpost;
            }
        }
    }
    return $highest;
    }