Scala使用Future.sequence进行期货，但在返回元组时出现问题

Question

当我使用下面的Future.sequence时，我在尝试返回元组时遇到了一些问题：

type UserId = Int
type GameId = Int
type Score = Double
case class Game(id: GameId)
def findGame(id: GameId): Future[Game] = ???
def findUserGames(id: UserId): Future[Seq[(GameId, Score)]] = ???
def findGames(id: UserId): Future[Seq[(Game, Score)]] = {
val userGames = findUserGames(id)
// ******* I am stuck here
val games: Future[Seq[Game]] = userGames.flatMap(x => Future.sequence(x.map(y => findGame(y._1))))    
}

当Future.sequence调用只返回Seq[Game]时，我如何返回(Game, Score)的元组？

此外，如果我们没有Future.sequence，我们如何能够模仿它的作用？即将CCD_ 5转换为CCD_？

Answer 1

你可以试试这个：

def findGames(id: UserId): Future[Seq[(Game, Score)]] = {
findUserGames(id).flatMap(gameIdToScoreSeq =>
Future.traverse(gameIdToScoreSeq)(gameIdToScore =>
findGame(gameIdToScore._1).map((_, gameIdToScore._2))
)
)
}

Answer 2

只需跟踪名称，作为一个oneliner，您就可以进行

def findGames(id: UserId)(implicit ec: ExecutionContext): Future[Seq[(Game, Score)]] =
findUserGames(id).flatMap(games =>
Future.sequence(games.map { case (gameid, score) =>
findGame(gameid).map(game => game -> score)
})
)

Answer 3

您只需要多一张地图：

val games: Future[Seq[(Game, Score)]] = userGames.flatMap(x => Future.sequence(x.map(y => findGame(y._1).map(z => (z, y._2)))))

正如你所看到的，它变得有点复杂。通过使用进行理解和模式匹配，您可以使代码更可读(可以说(

val games2: Future[Seq[(Game, Score)]] = for {
games <- userGames
result <- Future.sequence(games.map {
case (gameId, score) => 
for {
game <- findGame(gameId)
} yield (game, score)
})
} yield result