循环处理期货(Deal with futures in a loop)

 我正在研究对数据库进行查询并占用一行的方法。 该行有一列指定了父代码（如果有的话）。 所以，我的方法有一个名为“iterate”的闭包，如果最后一行有一个父进程，那么它会执行相同的过程，最后该方法返回这些行的Sequence。 这很简单，但我必须处理期货和那些东西，我对异步编程没有多少经验。 所以。 我的问题是： 
 
 有没有办法在不使用“Await”的情况下正确地执行此方法？ 
 
/**
   * Returns all the parents of the given sector if any
   * @param childSector
   * @return
   */
  def getParents(childSector: ShopSector): Future[Option[Seq[ShopSector]]] = {
    val p = Promise[Option[Seq[ShopSector]]]
    val f: Future[Option[Seq[ShopSector]]] = p.future

    val parentsSeq: Seq[ShopSector] = Seq()

    f.onComplete( thing => println(s"Result from Iteration future: $thing") )

    def iterate(sector: ShopSector): Unit = {
      val query = for {
        c <- ShopSectors if c.id === sector.id
        p <- c.parent
      } yield p

      exists(sector.parent_id).map { exists =>
        if (exists) {
          db.run(query.result.head).map { parent =>
            println(s"Result parent: $parent")
            parentsSeq +: Seq(parent)
            iterate(parent)
          }
        } else {
          p success Option(parentsSeq)
        }
      }
    }

    iterate(childSector)

    f
  }
 
 顺便说一句，我正在使用Slick。 并注意到这种方法效果不佳。 它返回一个空的Seq，我知道很明显这会返回它。 但印刷品工作正常并打印出正确的结果。 问题是我无法想象在所有期货完成之前有一个不会“消失”的变量的方法。 
 
 提前致谢。 
 
 编辑：好的伙计们。 问题很简单。 正如Ixx所说，parentsSeq集合并不可变。 我通过使用ListBuffer然后将其转换为序列来修复它。 

I am working on a method that makes a query to the database and takes one row. This row has a column specifying the parent id if any. So, my method has a closure named "iterate" that do the same process if the last row has a parent and finally the method returns a Sequence of those rows. This is simple at first sight, but I have to deal with futures and that stuff and I do not have much experience with async programming. So. My question is:
 
Is there a way to do this method right without the use of "Await"?
 
/**
   * Returns all the parents of the given sector if any
   * @param childSector
   * @return
   */
  def getParents(childSector: ShopSector): Future[Option[Seq[ShopSector]]] = {
    val p = Promise[Option[Seq[ShopSector]]]
    val f: Future[Option[Seq[ShopSector]]] = p.future

    val parentsSeq: Seq[ShopSector] = Seq()

    f.onComplete( thing => println(s"Result from Iteration future: $thing") )

    def iterate(sector: ShopSector): Unit = {
      val query = for {
        c <- ShopSectors if c.id === sector.id
        p <- c.parent
      } yield p

      exists(sector.parent_id).map { exists =>
        if (exists) {
          db.run(query.result.head).map { parent =>
            println(s"Result parent: $parent")
            parentsSeq +: Seq(parent)
            iterate(parent)
          }
        } else {
          p success Option(parentsSeq)
        }
      }
    }

    iterate(childSector)

    f
  }
 
I am using Slick by the way. And notice that this method is not working well. It returns an empty Seq and I know it is obvious that this is going to return that. But the print works fine and print the right results. The thing is that I can't imagine a way to have a variable that doesn't "disappear" before all the futures are completed.
 
Thanks in advance.
 
EDIT: Okay guys. The problem was so simple. As Ixx said, the parentsSeq collection is not mutable. I fixed it by using a ListBuffer and then by converting it to a sequence.

原文：https://stackoverflow.com/questions/31761961