I realize this is well-trodden ground, but it's still a bit confusing for
newcomers.
Can we agree that the ask pattern is legitimate at the boundary between a
service and repository/DAO?
It seems to me that it is reasonable to want to abstract away the
persistence layer in a way that doesn't *assume* actors. ie:
trait UserDAOBlocking {
def getUser(id:UserId):Try[User]
}
and/or
trait UserDAOAsync {
def getUser(id:UserId):Future[User]
}
Now perhaps an implementation of UserDAOAsync would use an actor and
perhaps another would use Future { ...}
Perhaps the actor (UserDAOActor) would inject an implementation of
UserDAOBlocking.
Now suppose your client code *is* actor-aware. Then you might wish to use a
UserDAOActor directly.
In the following sample:
https://github.com/lucperkins/spray-akka-slick-postgres/blob/master/src/main/scala/app/server/TaskService.scala
he uses an actor (accessed directly in the Spray route) as follows
val postgresWorker = actorRefFactory.actorOf(Props[PostgresActor],
"postgres-worker")
def postgresCall(message: Any) =
(postgresWorker ? message).mapTo[String].map(result => result)
val taskServiceRoutes = {
pathPrefix("tasks") {
path("") {
get { ctx =>
ctx.complete(postgresCall(FetchAll))
} ~
Note the ask pattern. Still OK?
The PostgresWorker actor in this sample sends its results back to sender
case FetchTask(id: Int) =>
sender ! TaskDAO.fetchTaskById(id)
https://github.com/lucperkins/spray-akka-slick-postgres/blob/master/src/main/scala/app/actors/PostgresActor.scala
I'm wondering if there's a way to have two versions of this actor so that
it can be used with both ask() and in a chaining fashion? It looks as
though ask() does not have the equivalent of the version of tell that takes
an explicit sender ref. Perhaps mix in a behaviour trait with a function
that creates a Receive partial function, with the resultHandler as a
parameter?
def queryMessages(resultHandler:ActorRef):Receive = {
...
]
Hmm.
Thanks.
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