public function StudList($groupid)
 {
     $groupid = intval($groupid);
     if (isset($this->_cache['StudList'][$groupid])) {
         return $this->_cache['StudList'][$groupid];
     }
     $list = $this->models->InstanceClass('StudList');
     $rows = RecordBookQuery::StudList($this->db, $groupid);
     while ($d = $this->db->fetch_array($rows)) {
         $list->Add($this->models->InstanceClass('StudItem', $d));
     }
     return $this->_cache['StudList'][$groupid] = $list;
 }