将Scala选项[Future [T]]转换为Future [Option [T]] [英] Scala Option[Future[T]] to Future[Option[T]]

问题描述

如何在Scala中将Option[Future[T]]转换为Future[Option[T]]?

How can I convert Option[Future[T]] to Future[Option[T]] in scala?

我想在以下地方使用它:

I want to use it in:

val customerAddresses = for {
  a <- addressDAO.insert(ca.address) // Future[Address]
  ia <- ca.invoiceAddress.map(addressDAO.insert) // Option[Future[Address]]
} yield (a, ia) // Invalid value have to be two futures

此处签名插入方法

def insert(address: Address): Future[Address]

ca是一个CustomerData

ca is a CustomerData

case class CustomerData(address: Address, invoiceAddress: Option[Address])

推荐答案

import scala.concurrent.Future
import scala.concurrent.ExecutionContext

def f[A](x: Option[Future[A]])(implicit ec: ExecutionContext): Future[Option[A]] = 
  x match {
     case Some(f) => f.map(Some(_))
     case None    => Future.successful(None)
  }

示例:

scala> f[Int](Some(Future.successful(42)))
res3: scala.concurrent.Future[Option[Int]] = Success(Some(42))

scala> f[Int](None)
res4: scala.concurrent.Future[Option[Int]] = scala.concurrent.impl.Promise$KeptPromise@c88a337

这篇关于将Scala选项[Future [T]]转换为Future [Option [T]]的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！