How do I compose nested case classes populated with async mongodb queries in play framework - scala

Question

I have been trying to convert mongodb queries I have working with await to using totally async. The problem is, I cannot find any examples or get code working to populate a list of objects where for each object there is a nested find returning futures.
I have seen examples for a single object, such as
val user = mongoDao.getUser(id)
val address = mongoDao.getAddress(user.id)
for that I see for comprehension works just fine. However, I have a list of objects (similar to users) and I cant seem to get the code right.
What I need to do is get all the users in an async manner, then when they complete, get all the addresses and populate a field (or create a new case class.)
val usersFuture : Future[List[User]] = mongoDao.getUsers()
val fullFutures : Future[List[FullUser]] = usersFuture.map(users: List[User] => {
users.map(user: User => {
val futureAddress : Future[Address] = mongoDao.getAddress()
// Now create a object
futureAddress.map(address: Address) {
FullUserInfo(user, address)
}
}
}
So, I'd like to end up with a Future[List[FullUser]] that I can return to the play framework. I've included the cutdown I've tried.
thanks
// OBJECTS HERE
case class Outer(id: Int, name: String)
case class Inner(id: Int, name: String)
case class Combined(id: Int, name: String, inner: Inner)
// FAKE DAO to reproduct
#Singleton
class StatInner #Inject()( implicit val ec: ExecutionContext) {
def outer() = {
Future {
val lb = new ListBuffer[Outer]()
Thread.sleep(1000)
println("Done")
for (id <- 1 to 5) {
lb += Outer(id, s"Hello $id")
}
lb.toList
}
}
def inner(id: Int) : Future[Inner] = {
Future {
Thread.sleep(1000)
Inner(id, s"inner $id")
}
}
}
// CODE to query that is not working
def nestedTree = Action.async {
val statInner : StatInner = new StatInner()
val listouter : Future[List[Outer]] = statInner.outer()
val combined = listouter.map((listOuter : List[Outer]) => {
listOuter.flatMap((outer: Outer) => {
val futInner : Future[Inner] = statInner.inner(outer.id)
futInner.map((inner: Inner) => {
Combined(outer, inner)
})
})
})
combined.map(Json.toJson(_))
}
```

Answer 1

Use Future.{flatMap.sequence}:
val usersFuture: Future[List[User]] = mongoDao.getUsers()
val fullFutures: Future[List[FullUser]] = usersFuture.flatMap { users =>
Future.sequence(users.map { user =>
mongoDao.getAddress().map { adress =>
FullUserInfo(user, address)
}
})
}