Scala Mongo driver getting results using Future

Question

I am intending to fetch all records that match a criteria from Mongo using Scala Mongo Driver .

Using Observables, you can access the stream by creating a subscription:

val MaxBuffer: Long = 100
var docs: Queue[Document] = Queue.empty
var sub: Option[Subscription] = None

val q: Observable[Document]

def fetchMoreRecords: Unit = sub.get.request(MaxBuffer)

q.subscribe(new Observer[Document] {

  override def onSubscribe(subscription: Subscription): Unit = {
    sub = Some(subscription)
    fetchMoreRecords
  }

  override def onError(e: Throwable): Unit = fail(out, e)

  override def onComplete(): Unit = {
    println("Stream is complete")
    complete(out)
  }

  override def onNext(result: Document): Unit = {
    if (doc.size == maxBuffer) {
      fail(out, new RuntimeException("Buffer overflow"))
    } else {
      docs = docs :+ result
    }
  }

})

(this code is incomplete)

I would need a function like:

def isReady: Future[Boolean] = {}

Which completes whenever onNext was called at least once. The bad way to do this would be:

def isReady: Future[Boolean] = {
    Future {
        def wait: Unit = {
            if (docs.nonEmpty) {
                true
            } else { wait }
        }
        wait
    }
}

What would be the best way to achieve this?

Answer 1

You want to use Promise :

 val promise = Promise[Boolean]()
 ...
 override def onNext() = {
   ...
   promise.tryComplete(Success(true))
}
override def onError(e: Throwable) = 
   promise.tryComplete(Failure(e))



val future = promise.future

You should do something to handle the case when there are no result (as it is now, the future will never be satisfied ...