public function getChildSkuSelectionMapping($childSku)
    {

        // query whether or not a child SKU selection ID mapping is available
        if (isset($this->childSkuSelectionIdMapping[$childSku])) {
            return $this->childSkuSelectionIdMapping[$childSku];
        }

        // throw an exception if the SKU has not been mapped yet
        throw new \Exception(
            $this->appendExceptionSuffix(
                sprintf('Found not mapped selection ID mapping for SKU %s', $childSku)
            )
        );
    }