如何将Twitter未来[Map [A​​,Future [C]]]转换为未来[Map [A​​,C]]

Question

我想解决以下问题:

我有一个未来[地图[A,B]].对于所有B,我需要应用一个将B转换为Future [C]的方法,并且我想要回馈Future [Map [A​​,C]]

这是我到目前为止的代码:

def getClients(clientIds: Seq[Int]): Future[Map[Int, ClientData]] = {

  def getClientData(clientInfo: ClientInfo): Future[ClientData] = 
    clientInfo match {
      case ValidInfo(info) => getData(info)
      case _ => throw new Exception
    }

  client.getClients(clientIds) map {
    _.toMap map {
      case (clientId: Int, clientInfo: ClientInfo) =>
        getClientData(clientInfo) map {
          clientData => (clientId, clientData)
      }
    }
  }
}

此代码错误,因为它返回Iterable [Future [(Int,ClientData)]]

对于info getClients是一个thrift方法,它返回Map [Map [A​​,B]],其中Map是可变的,所以我需要首先使用toMap将它转换为不可变的映射.

预先感谢您的帮助!

Answer 1

scala> def f: Future[Map[String, Future[Int]]] = ???
f: Future[Map[String,Future[Int]]]

scala> def x = for {
     |   m <- f
     |   i = m.map{ case (k, fv) => fv.map{ k -> _ } }
     |   l <- Future.sequence(i)
     | } yield l.toMap
x: Future[Map[String,Int]]

一步步:

转换Future[Map[A, Future[B]]]为Future[Iterable[Future[(A, B)]]]:

scala> def x1 = f.map{ _.map{ case (k, fv) => fv.map{ k -> _ } } }
x1: Future[Iterable[Future[(String, Int)]]]

转换Iterable[Future[(A, B)]]为Future[Iterable[(A, B)]]和flatten Future[Future[...]]使用flatMap:

scala> def x2 = x1.flatMap{ Future.sequence(_) }
x2: Future[immutable.Iterable[(String, Int)]]

转换Iterable[(A, B)]为Map[A, B]:

scala> def x = x2.map{ _.toMap }
x: Future[Map[String,Int]]

对于com.twitter.util.Future你应该使用collect的,而不是sequence和toSeq之前collect因为它接受Seq:

def x = for {
  m <- f
  i = m.map{ case (k, fv) => fv.map{ k -> _ } }
  l <- Future.collect(i.toSeq)
} yield l.toMap