如何使用MongoDB Scala驱动程序将聚合结果累积到集合中

我正在将我自己用Java编写的代码迁移到Scala，Scala在MongoDB中进行聚合。但是我被困在如何使用MongoDB Scala驱动程序在集合中累积聚合结果的问题上

Java代码：

mongoCollection.aggregate(aggregatePipeline)
    .map(document -> {
      Document group = document.get("_id", Document.class);
      return new Document("chat", group).append("count", document.get("count"));
    })
    .into(new ArrayList<>(), (results, e) -> {
      Document document = new Document("chats", results);
      System.out.println(document.toJson());
    });

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从Scala中的代码可以看出，我没有积累聚合结果，因为我不知道如何使用MongoDB Scala驱动程序从Java代码中的.into方法获得相同的行为。我在互联网上做了很多研究，但没有成功。如果有人能帮助我，我将不胜感激。

您应该特别使用隐式。还有一个toFuture方法可以有效地运行collect并在将来返回结果

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您可以设置Seq[Document]类型的变量，然后在订阅事件触发后将生成的文档序列附加到该变量。使用承诺/未来等待结果。例如：

def find_all (collection_name: String): Seq[Document] = {

    /* The application will need to wait for the find operation thread to complete in order to process the returned value. */

    log.debug(s"Starting database find_all operation thread")

    /* Set up new client connection, database, and collection */
    val _client: MongoClient = MongoClient(config_client)
    val _database: MongoDatabase = _client.getDatabase(config_database)
    val collection: MongoCollection[Document] = _database.getCollection(collection_name)

    /* Set up result sequence */
    var result_seq : Seq[Document] = Seq.empty

    /* Set up Promise container to wait for the database operation to complete */
    val promise = Promise[Boolean]

    /* Start insert operation thread; once the thread has finished, read resulting documents. */
    collection.find().collect().subscribe((results: Seq[Document]) => {
      log.trace(s"Found operation thread completed")
      /* Append found documents to the results */
      result_seq = result_seq ++ results
      log.trace(s" Result sequence: $result_seq")

     /* set Promise container */      
     promise.success(true)

     /* close client connection to avoid memory leaks */
      _client.close
     })

    /* Promise completion result */
    val future = promise.future

    /* wait for the promise completion result */
    Await.result(future, Duration.Inf)
    /* Return document sequence */
    result_seq

  }

---

或者你可以看一看注释：ReactiveMongo不支持MongoDB的所有最新功能

mongoCollection.aggregate(aggregatePipeline)
    .map[Document](doc => Document("chat" -> doc.get("_id"), "count" -> doc.get("count")))
    .collect()
    .subscribe((docs: Seq[Document]) => println(docs))

def find_all (collection_name: String): Seq[Document] = {

    /* The application will need to wait for the find operation thread to complete in order to process the returned value. */

    log.debug(s"Starting database find_all operation thread")

    /* Set up new client connection, database, and collection */
    val _client: MongoClient = MongoClient(config_client)
    val _database: MongoDatabase = _client.getDatabase(config_database)
    val collection: MongoCollection[Document] = _database.getCollection(collection_name)

    /* Set up result sequence */
    var result_seq : Seq[Document] = Seq.empty

    /* Set up Promise container to wait for the database operation to complete */
    val promise = Promise[Boolean]

    /* Start insert operation thread; once the thread has finished, read resulting documents. */
    collection.find().collect().subscribe((results: Seq[Document]) => {
      log.trace(s"Found operation thread completed")
      /* Append found documents to the results */
      result_seq = result_seq ++ results
      log.trace(s" Result sequence: $result_seq")

     /* set Promise container */      
     promise.success(true)

     /* close client connection to avoid memory leaks */
      _client.close
     })

    /* Promise completion result */
    val future = promise.future

    /* wait for the promise completion result */
    Await.result(future, Duration.Inf)
    /* Return document sequence */
    result_seq

  }