Akka jackson-json serialization-bindings has issue in deserializing scala tuples

Question

In my usecase, I have a SourceEvent case class which can take an instance of a generic type as a parameter like this:

case class SourceEvent[T](event: T, hash: Int = 0) extends Command 

When the SourceEvent is being constructed, T is being passed as a Tuple2 like:

SourceEvent[(String,String)](("abc","sample-event"), hash = "sample-event".hashCode) 

When this is received by a Behavior, tuple is being treated as list like this:

message match {
      case m: SourceEvent[(String,String)] =>
context.log.info(s"Message received : ${m}")
Behaviors.same
}

It's printing the below log:

Message received : SourceEvent(List(abc,sample-event),-1486933305)

While trying to access any fields for the tuple like m.event._1, the below exception is being thrown:

[local-test-akka.actor.default-dispatcher-5] ERROR akka.actor.SupervisorStrategy - scala.collection.immutable.$colon$colon cannot be cast to scala.Tuple2

How do we deserialize a Tuple as it is using jackson-json serialization in akka!!

Answer 1

I have not worked much with fasterxml.jackson library, but I think there are some few points that you should consider.

• First of all is that be aware of type erasure, take a look at this question. If you have noticed, here a SourceEvent[List[String]] is matched as SourceEvent[(String, String)] although you did not want it.
• Second thing, as I mentioned earlier, I have not worked much with fasterxml.jackson library, but as far as I know, you can define your own custom serializer/deserializers. So you can parse the tuple type manually.
• Since there is no standard way of representation of tuples in JSON, it is serialized/deserialized to/from arrays. And since tuples are entities that orders of elements matters a lot in them, I suggest you use a safer approach, like modeling your data. For instance, you think the first element of your tuple is the name, and the second one is the country of a person, what if you somehow received ["USA", "John"]? so modeling can help a lot in your case, i.e,. {"name":"John","country":"USA"}