Domain Driven Design: Domain Service, Application Service

Question

Can someone explain the difference between domain and application services by providing some examples? And, if a service is a domain service, would I put the actual implementation of this service within the domain assembly and if so, would I also inject repositories into that domain service? Some info would be really helpful.

Answer 1

Services come in 3 flavours: Domain Services, Application Services, and Infrastructure Services.

• Domain Services : Encapsulates business logic that doesn't naturally fit within a domain object, and are NOT typical CRUD operations – those would belong to a Repository.
• Application Services : Used by external consumers to talk to your system (think Web Services). If consumers need access to CRUD operations, they would be exposed here.
• Infrastructure Services : Used to abstract technical concerns (e.g. MSMQ, email provider, etc).

Keeping Domain Services along with your Domain Objects is sensible – they are all focused on domain logic. And yes, you can inject Repositories into your Services.

Application Services will typically use both Domain Services and Repositories to deal with external requests.

Hope that helps!