public function getVoucherNrList()
    {
        $oDb = \OxidEsales\Eshop\Core\DatabaseProvider::getDb(\OxidEsales\Eshop\Core\DatabaseProvider::FETCH_MODE_ASSOC);
        $aVouchers = [];
        $sSelect = "select oxvouchernr from oxvouchers where oxorderid = " . $oDb->quote($this->oxorder__oxid->value);
        $rs = $oDb->select($sSelect);
        if ($rs != false && $rs->count() > 0) {
            while (!$rs->EOF) {
                $aVouchers[] = $rs->fields['oxvouchernr'];
                $rs->fetchRow();
            }
        }

        return $aVouchers;
    }