public function setObjId($objId)
    {
        if (!is_scalar($objId)) {
            throw new InvalidArgumentException(sprintf(
                'Object ID must be a string or numerical value, received %s.',
                (is_object($objId) ? get_class($objId) : gettype($objId))
            ));
        }

        $this->objId = $objId;

        return $this;
    }