How to return the values of a query using the observer pattern

Question

I am new in this Scala world and I would be thankful if someone could help me. So, I am building a Scala application that saves files to a mongodb database using the MongoDB Scala driver. I was using Casbah before, but since it says in the mongodb official website that it is a legacy driver and my project has just started, I decided to move to the official driver.

So my application saves an Object that contains an id and this id comes to a collection from MongoDB called "Sequences". Every time I wanna save an object from this class, it first will get the last id from the sequence and increment it by one.

When I was using Casbah, this code used to do the job:

def getSequenceId(seqName: String): Int = {
  val query = MongoDBObject("seq_id" -> seqName);
  val result = MongoFactory.SequenceCollection
                          .findAndModify(query, $inc("nextId" -> 1)) 
  val nbr = result.get("nextId");
  return nbr.toString.toDouble.toInt;
}

The problem is that with the MongoDB Scala driver, you have to use the Observable pattern for that and I am a bit confused.

So far, I managed to make a code like this:

def getSequenceId(seqName: String): Int = {
  val query = new BsonDocument("seq_id", new BsonString(seqName))
  val resultado = NewMongo.SequenceCollection.findOneAndUpdate(query,inc("nextId",1)).collect()          
   .subscribe(new Observer[Seq[Document]] {
      override def onNext(result: Seq[Document]): Unit = println(s"UPDATED ${result(0)}")
      override def onError(e: Throwable): Unit = println(s"Failed due to $e")
      override def onComplete(): Unit = println("Completed")
  })
}

The problem is that this is my first time to use this Observer pattern and I don't know how to get the modified document to get the last id. I searched in a lot of websites about it and I couldn't find an answer. In most cases I only found solutions for Casbah.

Thanks

score 1 · Accepted Answer · answered Feb 09 '17 at 07:07

Just for the sake of clarification, I found out how to do it myself:

def getSequenceId(seqName: String): Int = {

  val query = new BsonDocument("seq_id", new BsonString(seqName))    
  val resultado = NewMongo.AibodSequence.findOneAndUpdate(query,inc("nextId",1))    
  resultado.subscribe(new Observer[Document] {        
    override def onNext(result: Document): Unit ={}
    override def onError(e: Throwable): Unit ={}
    override def onComplete(): Unit = {}
  })
  val awaitedR = Await.result(resultado.toFuture, Duration.Inf).asInstanceOf[List[Document]](0)

  val ret = awaitedR.get("nextId").getOrElse(0).asInstanceOf[BsonDouble].intValue();

  return ret;  
}

Apparently you can convert the result observer into a future and wait for its return using the Await function as I did. Then you can manipulate the result as you wish.

I am a bit late to the game but is there a reason you didn't simply collect and subscribe in this case to get the data as a Seq? I am not sure how they built Observables behind the doors but surely all this casting have downsides — sinanspd, Aug 08 '18 at 04:58

score 0 · Answer 2 · answered Feb 07 '17 at 10:07

0

You should use ReactiveMongo .It's simply the best scala driver for mongo out there. And if you are using play framework, use the ReactiveMongo play extension.

answered Feb 07 '17 at 10:07

oblivion

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Hello oblivion, thanks for your reply. My idea was to use the official MongoDB driver. That's why I asked the question. I already have the answer by using another library. – Israel Zinc Feb 08 '17 at 02:36

How to return the values of a query using the observer pattern

2 Answers2