Scala, play framework: How to properly inject dependency in domain (entity) class

Question

I have an domain object:

case class User(val id: Long, username: String)

I don't want to follow service-repository approach (like typical spring applications, where entities are just data holders), I want to put functionality related to user into User object.

But I don't want to tie User object to concrete infrastructure implementations, so I want to pass interfaces (traits) instead.

I'm trying do this by following way:

case class User(val id: Long, val username: String, implicit val userRepository: IUserRepository)

And somewhere in application (controller, or somewhere else), I want to inject (with @Inject()) concrete implementation of IUserRepsoitory and want it to implicitly passed to constructor of User.

Question 1: case class User(val id: Long, val username: String, implicit val userRepository: IUserRepository) - this doesn't work, it is not compiled

Question 2: Is it correct approach to decouple infrastructure implementation from object domain in play? are they some best practices?

Thanks.

That's subjective, but for Q2 I would generally say "no", the domain object should not know how the application is managing it, according the context. — cchantep
What do you mean? Is it bad practice if User (domain object) interacts with repository interface? (not implementation) — Teimuraz
Why? Do you prefer entities to be just data holder? Just I'd like follow ddd approach (not 100%), more OO approach.. Why is it bad? — Teimuraz
For me, case class are designed to represent data, not process — cchantep

Martijn Martijn · Accepted Answer · 2016-07-11T14:15:37

An entire parameter list is either implicit or not. You're looking for

case class User(id: Long, username: String)(implicit userRepository: IUserRepository)

Architecturally, it sounds like a bad idea to have a user class know it's own repository.

Scala, play framework: How to properly inject dependency in domain (entity) class

1 Answers