Order (DTO) containing all relevant information of a Customer and her Products.
The id of the client (one of @link OrderClient) who has last modified this order.
The Customer who has placed this order. Must not be null.
The id of an order. It is a number which is generated by a sequence (see Counter.
The key of the preferred language (either „de“ or „en“) of the Customer. Must not be empty.
List of data Products the Customer want to order.
The current state of the order. One of OrderState.