Question

我在调用另一个从Future.traverse中返回Future的函数时遇到了麻烦。场景是我有一个Seq [Document]，我需要将它们变成Future [Seq [NewsArticle]]。但是，为了做到这一点，我需要使用doc.categoryID并使用它来调用另一个API来构建NewsCategory，它将作为Future [NewsCategory]返回。我的问题是不知道如何在返回之后将其压入Future.traverse 。

到目前为止，这是我的scala代码：

object NewsArticle { def buildNewsArticles(docs:Seq[Document]):Future[Seq[NewsArticle]] = { Future.traverse(docs) { doc => val categoryID = doc.catID val title = doc.title val pdf = doc.pdfLink val image = doc.imageUrl val body = doc.body //need to call NewsCategory.buildNewsCategory(categoryID) //but it returns a Future[NewsCategory] //can't use for-yield because it still only yields //a Future future(NewsArticle( ??? ,title, pdf, image, body) } } } object NewsCategory { def buildNewsCategory(catID:String):Future[NewsCategory] = { // Calls external api across the wire and // Returns a Future[NewsCategory] } } // CASE CLASSES case class NewsArticle( category:NewsCategory, title:String, pdf:String, image:String, body:String) case class NewsCategory( id:String, name:String description:String)

感谢您的帮助

Answer 1

听起来您希望根据NewsArticle中未来返回的NewsCategory创建buildNewsCategory实例，这意味着您处于正确的轨道上。我认为以下内容可以满足您的需求：

Future.traverse(docs) { doc => 
    val categoryID = doc.catID
    val title = doc.title
    val pdf = doc.pdfLink
    val image = doc.imageUrl
    val body = doc.body

    // This could be a for-yield instead as you note.
    NewsCategory.buildNewsCategory(categoryID).map { category =>
      NewsArticle(category, title, pdf, image, body)
    }
 }

Answer 2

也许试试这个：

object NewsArticle {

  def buildNewsArticles(docs:Seq[Document]):Future[Seq[NewsArticle]] = {
     Future.traverse(docs) { doc => 
        val categoryID = doc.catID
        val title = doc.title
        val pdf = doc.pdfLink
        val image = doc.imageUrl
        val body = doc.body

        for {
          cat <- NewsCategory.buildNewsCategory(categoryID)
        } yield new NewsArticle(cat, title, pdf, image, body)

     }
  }
}

从Future.traverse中开始另一个Future调用

2 个答案: