public function storageVal($val)
    {
        $val = $this->dateTimeVal($val);

        if ($val instanceof DateTimeInterface) {
            return $val->format('Y-m-d H:i:s');
        } else {
            if ($this->allowNull()) {
                return null;
            } else {
                throw new Exception(
                    'Invalid date/time value. Must be a DateTimeInterface instance.'
                );
            }
        }
    }