public function getTaxClassIdByTaxClassName($taxClassName)
    {

        // query whether or not, the requested tax class is available
        if (isset($this->taxClasses[$taxClassName])) {
            return (integer) $this->taxClasses[$taxClassName][MemberNames::CLASS_ID];
        }

        // throw an exception, if not
        throw new \Exception(
            $this->appendExceptionSuffix(
                sprintf('Found invalid tax class name %s', $taxClassName)
            )
        );
    }