public function getJsonRows(
        array $arrWhat = ['*'], 
        array $arrWhere = [], 
        array $arrOrder = ['`id` ASC'], 
        array $arrLimit = []
    ) : string
    {
        $rows = $this->loadByPrepStmt($arrWhat, $arrWhere, $arrOrder, $arrLimit);
        $json = json_encode($rows, JSON_UNESCAPED_UNICODE);
        return $json;
    }