private static function _extractWhereAssociativeConditions($conditions, $cls, $escape)
    {
        $temp_cond = "";
        foreach ($conditions as $key => $value) {
            $temp_cond .= "$escape".self::getTableName()."$escape.$escape".self::$_mapping[$cls][$key]."$escape=? and ";
        }
        return substr($temp_cond, 0, strlen($temp_cond)-5);
    }