Scala's Cake Patten Example

example.scala

// This is all write by hand and probably has typos. 
// The general idea is to show how it composes and how other
// system that extend the core services can choose which implementations
// of the coreservice DAOs to use
trait CoreServiceDaos {
  val logDao: LogDao
  val healthDao: HealthDao
}


trait BaseCoreActors {
   this: Core with CoreServiceDaos =>
   lazy val statusActor = system.actorOf(Props[StatusServiceActor])
   lazy val healthActor = system.actorOf(Props(new HealthActor(healthDao), "health-actor"))
   lazy val logActor = system.actorOf(Props(new LogActor(logDao), "log-actor")
 }

trait BaseServiceRoutes extends RouteConcatenation{
  this: BaseCoreActors with Core with CoreServiceDaos =>

  // 
  val logDao = new InMemoryDao
  // val logDao = new LogSqlDao(dbconfig)
  val gauges = Seq(HealthGauge("my-gauge", "name", "Desc"))
  val healthDao = new HealthDao(gauges)
  
  // Create my Services
  val baseServices = Seq(
    new StatusService(statusActor),
    new SubSystemResourceService(),
    new SubSystemConfigService(),
    new SubSystemComponentService(),
    new LogService(logActor),
    new HealthService(healthActor))

}
trait Api extends RouteConcatenation with BaseServiceRoutes{
  this: BaseCoreActors with Core with CoreServiceDaos =>

  private implicit val _ = system.dispatcher

  val manifestService = new ManifestService(baseServices.map(x => x.manifest))

  def mergeRoutes(a: Route, b: Route): Route = {
    a ~ b
  }

  val routes = baseServices.map(i => i.routes).fold(manifestService.routes)(mergeRoutes)

  val rootService = system.actorOf(Props(new RoutedHttpService(routes)))

}

extending.scala

trait SecondaryAnalysisApi extends BaseServiceRoutes {
  this: SecondaryCoreActors with Core with CoreServiceDaos with EngineSystemConfig with PipelineTemplateConfig =>

  private implicit val _ = system.dispatcher

   // I can still decide which implementation of the core service Actor Daos here.
  val logDao = new InMemoryDao
  // val logDao = new LogSqlDao(dbconfig)
  val gauges = Seq(HealthGauge("my-gauge", "name", "Desc"), 
  HealthGauge("my-extended-system-gauge", "name", "Desc"))
  val healthDao = new HealthDao(gauges)
  
  // pull in base services without changing anything
  val subSystemServices = baseServices ++ Seq(
    new SecondaryAnalysisServiceStatus(),
    new JobManagerService(dbActor, engineManagerActor, engineConfig),
    new JobEngineService(engineManagerActor, engineDaoActor, engineConfig),
    new DataSetService(dbActor),
    new PipelineTemplateService(pipelineTemplateActor),
    new DataSetImportService(dbActor))

  lazy val manifestService = new ManifestService(subSystemServices.map(x => x.manifest))

  def mergeRoutes(a: Route, b: Route): Route = {
    a ~ b
  }

  val routes = subSystemServices.map(i => i.routes).fold(manifestService.routes)(mergeRoutes)

  // For backward compatibility in the tests
  val totalRoutes = routes

  val rootService = system.actorOf(Props(new RoutedHttpService(routes)))

}