Hi,

I was wondering if anyone had anymore thoughts about validation.

I've been enhancing the domain model from POJOs in Action to do more sophisticated validation and return multiple errors. Instead of throwing an exception when the first error is detected the code now returns a collection of errors in a Notification.

For example, the business logic for processing the delivery information for an order has to verify two things:

1. The delivery time is one hour in the future
2. The delivery time and address is served by can at least one restaurant

Several things can be wrong:

·         Delivery time is not far enough in the future

·         No restaurants serve the delivery address

·         No restaurants serve the delivery time

·         No restaurants serve the combination of delivery time and address

The domain logic now accumulates these errors in a Notification.

One observation I would make is doing more elaborate validation makes the code more complicated – not surprising since its doing more. E.g. there is additional code to figure out whether it's the delivery time or delivery address are wrong. The Notification also has to be passed around between domain objects, e.g. from the PlaceOrderService, which ultimately returns it to the client, to the PendingOrder to the DeliveryInfo.

Much of the validation logic is currently in the DeliveryInfo class, which has a validate() method:

class DeliveryInfo {

  private Address deliveryAddress;

  private Date deliveryTime;

 void validate(Notification, RestaurantRepository) {

  ….

 }

 …

}

The validate() method checks that the delivery time is in the future and calls RestaurantRepository to determine whether the deliveryInfo is served by any restaurants. I suppose that I could, instead, have a separate DeliveryInfoValidator class.

Any thoughts?

Chris