play-2.0-cake.scala

// my response to https://groups.google.com/forum/?fromgroups#!searchin/play-framework/cake/play-framework/LQ2y40QNZaE/qvRFw5of-rQJ

import play.api._
import play.api.mvc._

// Domain object
case class User(id: String, name: String)

// Trait defining the service component
trait UserServiceComponent {
    trait UserService {
        def getUserName(id: String): String
    }

    val userService: UserService
}

// Real implmentation
trait RealUserServiceComponent extends UserServiceComponent {

    // Explicit dependency on User Repository
    self: UserRepositoryComponent =>

    override val userService: UserService = new UserService {
        // Use the repository in the service
        override def getUserName(id: String) = userRepository.getUser(id).name
    }
}

// Trait defining the repository
trait UserRepositoryComponent {
    trait UserRepository {
        def getUser(id: String): User
    }

    val userRepository: UserRepository
}

// Real implmentation of repository
trait RealUserRepositoryComponent extends UserRepositoryComponent {
    override val userRepository: UserRepository = new UserRepository {
        override def getUser(id: String) = error("todo") // i.e to database, etc.
    }
}

// Fake implmentation of the repository
trait MockUserRepositoryComponent extends UserRepositoryComponent {
    override val userRepository: UserRepository = error("todo") // i.e. mock[UserRepository]
}


// Both of these "environments" are just mixins of the component traits.
// Therefore, they have as member variables all services and dependencies.
// All dependencies are compile checked - if a mixin is needed but not provided, the code won't compile.

// "Real" top level environment usable in controllers.
object real extends RealUserServiceComponent with RealUserRepositoryComponent

// "Fake" top level environment usable in controllers.
object fake extends RealUserServiceComponent with MockUserRepositoryComponent

// Use the real environment in the top level controller
object Application extends Controller {

    val userService = real userService

    def name(id: String) = Action {
        Ok(userService.getUserName(id))
    }

}

// Use the fake environment in the test.
class SomeTest {

    val userService = fake userService

    def sometTest {
        // set up the mock ...
        val name = userService.getUserName("id1")
        // do assertion
    }
}

// Or you can define the components add hoc.
class SomeOtherTest extends RealUserServiceComponent with UserRepositoryComponent {
    override val userRepository = error("todo") // mock or something

    def someOtherTest {
        // set up the mock
        val name = userService.getUserName("id2")
        // do assertion
    }
}