我正在使用Scala和Play框架构建响应式网站,我的数据模型常常需要组合Future
和Option
,并从先前的值构建List
/Set
的Future
以获取所需的结果。
我编写了一个简单的应用程序,使用虚拟数据源,您可以复制并粘贴它,然后应该能够编译。我的问题是,如何以可消耗的形式获取返回结果,即我的UserContext
。目前,我得到的是Future[Option[Future[UserContext]]]
。
我想要在纯Scala中做到这一点,以更好地学习该语言,因此我目前避免使用Scalaz。尽管我知道最终应该使用它。
package futures
import scala.concurrent.{Future, ExecutionContext}
// http://www.edofic.com/posts/2014-03-07-practical-future-option.html
case class FutureO[+A](future: Future[Option[A]]) extends AnyVal {
def flatMap[B](f: A => FutureO[B])(implicit ec: ExecutionContext): FutureO[B] = {
FutureO {
future.flatMap { optA =>
optA.map { a =>
f(a).future
} getOrElse Future.successful(None)
}
}
}
def map[B](f: A => B)(implicit ec: ExecutionContext): FutureO[B] = {
FutureO(future.map(_ map f))
}
}
// ========== USAGE OF FutureO BELOW ============= \\
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.Future
object TeamDB {
val basketballTeam = Team(id = 111, player_ids = Set(111, 222))
val baseballTeam = Team(id = 222, player_ids = Set(333))
def findById(teamId: Int): Future[Option[Team]] = Future.successful(
teamId match {
case 111 => Some(basketballTeam)
case 222 => Some(baseballTeam)
case _ => None
}
)
}
object PlayerDB {
val basketballPlayer1 = Player(id = 111, jerseyNumber = 23)
val basketballPlayer2 = Player(id = 222, jerseyNumber = 45)
val baseballPlayer = Player(id = 333, jerseyNumber = 5)
def findById(playerId: Int): Future[Option[Player]] = Future.successful(
playerId match {
case 111 => Some(basketballPlayer1)
case 222 => Some(basketballPlayer2)
case 333 => Some(baseballPlayer)
case _ => None
}
)
}
object UserDB {
// user1 is on BOTH the baseball and basketball team
val user1 = User(id = 111, name = "Michael Jordan", player_ids = Set(111, 333), team_ids = Set(111, 222))
// user2 is ONLY on the basketball team
val user2 = User(id = 222, name = "David Wright", player_ids = Set(222), team_ids = Set(111))
def findById(userId: Long): Future[Option[User]] = Future.successful(
userId match {
case 111 => Some(user1)
case 222 => Some(user2)
case _ => None
}
)
}
case class User(id: Int, name: String, player_ids: Set[Int], team_ids: Set[Int])
case class Player(id: Int, jerseyNumber: Int)
case class Team(id: Int, player_ids: Set[Int])
case class UserContext(user: User, teams: Set[Team], players: Set[Player])
object FutureOptionListTest extends App {
val result = for {
user <- FutureO(UserDB.findById(userId = 111))
} yield for {
players: Set[Option[Player]] <- Future.traverse(user.player_ids)(x => PlayerDB.findById(x))
teams: Set[Option[Team]] <- Future.traverse(user.team_ids)(x => TeamDB.findById(x))
} yield {
UserContext(user, teams.flatten, players.flatten)
}
result.future // returns Future[Option[Future[UserContext]]] but I just want Future[UserContext] or UserContext
}