function &fetch_valid_period_by_ids($ids_array, $params = array(), $sql_params = array())
 {
     $current_date = date('Y-m-d', time());
     $sql_params['conditions'][] = " AND tn.start_date <= '{$current_date}' AND tn.finish_date >= '{$current_date}' ";
     $result =& parent::fetch_by_ids($ids_array, $params, $sql_params);
     return $result;
 }