CODEWITHSUNDEEP
validationdomain-driven-design
Filip
Filip

Reputation: 1097

Validation in Domain Model of Domain Service?

I'm reading the book "Architecting Applications for the Enterpise (Dino Esposito)". It raised a question about validation.

The Domain Model can have a property CanBeSaved which calls the Validate() method of the Domain Model. All good, except for complex situations. For example a Customer model which needs a unique customer code (ex. 000542). You can only check this with database access. Isn't it better to put the Validation always in a Domain Service. So you have only one way of checking if an aggregate is in a valid state? If you use both, a developer can 'forget' to use the domain service validation for the Customer.

Upvotes: 1

Views: 712

Answers (1)

guillaume31
guillaume31

Reputation: 14080

I find it better to have always valid entities rather than rely on an external validation object.

That being said, unique checks are a bit of an exception since it is often not something that the aggregate itself can determine on its own, you have to look into all existing aggregates to see if the value is not already taken. What I do is check for availability of the value before creating the entity, and also put a constraint in the database which will verify uniqueness at persistence time. You could also try to find a domain concept that encompasses all your entities and make it an aggregate that has a list of all codes and enforces the uniqueness invariant.

Upvotes: 2

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