message goes to dead letter instead of sender (akka router) [scala] - akka

Question

Actually I`m having trouble with getting my actor (router) system to work correctly.
My Setup:
I`m trying to use an akka router within an play controller. For dependency injection I use scaldi.
scaldi module:
class UserDAOModule extends Module {
binding to new ExampleRouter
binding toProvider new UserDAOWorker
}
akka router:
class UserDAORouter(implicit inj:Injector) extends Actor with AkkaInjectable {
val userDAOProps = injectActorProps[UserDAOWorker]
var router = {
val routees = Vector.fill(5) {
val r = context.actorOf(userDAOProps)
context watch r
ActorRefRoutee(r)
}
Router(RoundRobinRoutingLogic(), routees)
}
override def receive: Receive = {
case mm: MongoDBMessage =>
router.route(mm, sender)
case Terminated(a) =>
router = router.removeRoutee(a)
val r = context.actorOf(userDAOProps)
context watch r
router = router.addRoutee(r)
}
}
worker:
class UserDAOWorker(implicit inj:Injector) extends Actor with Injectable {
val db = inject[DefaultDB]
val collection:JSONCollection = db("users")
val currentSender = sender
override def receive: Receive = {
case InsertUser(user) => insertUser(user)
}
def insertUser(user:User) = {
collection.save(user).onComplete {
case Failure(e) => currentSender ! new UserDAOReturnMessage(Some(e), None)
case Success(lastError) => currentSender ! new UserDAOReturnMessage(None, lastError)
}
}
}
When I send a message (insertUser message) to the router, it is routed correctly and the worker receives the message, but when the worker sends a message back to the sender it cant be delivered, so it is send to dead letter office. I cant figure out how to fix this. Is there someone able to help me?
Thanks in advance

Answer 1

I guess the problem is that the currentSender is initialized with null (i.e. ActorRef.noSender) in the constructor on actor creation. 'sender' is only valid in context of receiving a message in receive(). Sending a message to ActorRef.noSender is an equivalent of sending to dead letter queue.
Something like this should work:
class UserDAOWorker(implicit inj:Injector) extends Actor with Injectable {
val db = inject[DefaultDB]
val collection:JSONCollection = db("users")
override def receive: Receive = {
case InsertUser(user) => {
insertUser(sender, user)
}
}
def insertUser(currentSender : ActorRef, user:User) = {
collection.save(user).onComplete {
case Failure(e) => currentSender ! new UserDAOReturnMessage(Some(e), None)
case Success(lastError) => currentSender ! new UserDAOReturnMessage(None, lastError)
}
}
}