/**
  * @access private
  */
 protected function _prepare_restrictions()
 {
     parent::_prepare_restrictions();
     if (!$this->_returns_no_data()) {
         include_once 'webcore/db/query_security.php';
         $restriction = new QUERY_SECURITY_RESTRICTION($this, $this->_user);
         $sql = $restriction->as_sql(array(Privilege_set_folder));
         if (!$sql) {
             $this->_set_returns_no_data();
         } else {
             $this->_calculated_restrictions[] = $sql;
         }
     }
 }