使用 ReactiveMongo 的嵌套查询

Question

我有一个文章集，其中字段 "title" 和 "publication" 具有唯一的组合键约束。

当调用 insertOrUpdateArticle(a: Article) 时，它将首先尝试插入它，以防它遇到约束，它应该更新文章 - 如果需要的话。

然而，我在那之前卡住了。当前错误是：

Error:(88, 57) type mismatch;
 found   : scala.concurrent.Future[scala.concurrent.Future[Boolean]]
 required: Boolean
            col_article.find(selector).one[Article].map {

来源：

def insertOrUpdateArticle(a: Article): Future[Boolean] = {
  // try insert article
  col_article.insert[Article](a).map {
    // article inserted
    lastError => {
      println("Article added.")
      true
    }
  }.recover {
    case lastError: LastError =>
      // check if article existed
      lastError.code.get match {
        case 11000 => {
          // article existed (duplicate key error)

          // load old article
          val selector = BSONDocument(
            "title" -> BSONString(a.title),
            "publication" -> BSONString(a.publication)
          )

          col_article.find(selector).one[Article].map {
            case Some(old_a: Article) => {
              // TODO: compare a with old_a
              // TODO: if a differs from old_a, update
              Future(true)
            }
            case None => {
              // something went wrong
              Future(false)
            }
          }
        }
        case _ => {
          println("DB.insertOrUpdateArticle() unexpected error code when inserting: " + lastError.code.get)
          false
        }
      }
    case ex =>
      println("DB.insertOrUpdateArticle() unexpected exception when inserting: " + ex)
      false
  }
}

我不确定在这里做什么。如果文章被保存或更新，代码应该 return Future(true)，否则为 false。我在这里错过了 reactivemongo and/or scala 期货的一些东西。

Answer 1

使用recoverWith创建新的Future是解决方案，修改代码：

def insertOrUpdateArticleOld(a: Article): Future[Boolean] = {
  // try insert article
  col_article.insert[Article](a).map {
    // article inserted
    lastError => {
      println("Article added.")
      true
    }
  }.recoverWith {
    case lastError: LastError =>
      // check if article existed
      lastError.code.get match {
        case 11000 => {
          // article existed (duplicate key error)

          // load old article
          val selector = BSONDocument(
            "title" -> BSONString(a.title),
            "publication" -> BSONString(a.publication)
          )

          col_article.find(selector).one[Article].flatMap {
            case Some(old_a: Article) => {
              // TODO: compare a with old_a
              // TODO: if a differs from old_a, update
              Future(true)
            }
            case None => {
              // something went wrong
              Future(false)
            }
          }
        }
        case _ => {
          println("DB.insertOrUpdateArticle() unexpected error code when inserting: " + lastError.code.get)
          Future(false)
        }
      }
    case ex =>
      println("DB.insertOrUpdateArticle() unexpected exception when inserting: " + ex)
      Future(false)
  }
}

使用 ReactiveMongo 的嵌套查询

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