/**
  * 添加精华
  *
  * @param int $tid
  * @param array $fields
  * @return boolean
  */
 public function addThreadDigest(PwThreadDigestDm $dm)
 {
     if (true !== ($r = $dm->beforeAdd())) {
         return $r;
     }
     return $this->_getDao()->addThread($dm->tid, $dm->getData());
 }