playframework/play-json

Json reads fails for Map[K, V], where K is not a String.

WesselVS opened this issue · 3 comments

WesselVS commented

Are you looking for help?

This is an issue tracker, used to manage and track the development of Play JSON. It is not a support system and so it is not a place to ask questions or get help. If you're not sure if you have found a bug, the best place to start is with either the users mailing list or Stack Overflow.

If you want to discuss a feature request, the same tools are available.

Play JSON Version (2.5.x / etc)

2.9.2

API (Scala / Java / Neither / Both)

Scala

Operating System (Ubuntu 15.10 / MacOS 10.10 / Windows 10)

MacOS

JDK (Oracle 1.8.0_72, OpenJDK 1.8.x, Azul Zing)

Paste the output from java -version at the command line.

java version "11.0.9" 2020-10-20 LT

Expected Behavior

Please describe the expected behavior of the issue, starting from the first action.

  1. Given some json-convertible object o with type T, Json.fromJson[T](Json.toJson(o)) should yield the same o.
  2. For Map[(Int, Int), Int], this should be the case as well.

Actual Behavior

  1. Above property fails when using a Map[K, V], when K is not a String.
  2. This yield the error JsError(List((,List(JsonValidationError(List(error.expected.jsobject),List())))))

Reproducible Test Case

  println(Json.fromJson[Map[(Int, Int), Int]](Json.toJson(Map((1, 2) -> 1))))
WesselVS commented

Is this library still maintained?

BillyAutrey commented

Is this library still maintained?

Yes, it is.

BillyAutrey commented

To answer the issue more directly - the core library does not explicitly provide Reads or Writes for many types of K for Map[K,V]. In fact, the only types for K that this library provides for automatic JSON formatting are String and Char.

I don't know the historical reasons, but it feels like an intentional choice. And, when you consider what JSON keys look like, it makes sense.

In addition, if you want to Read or Write this type to JSON, play-json provides automatic formatters for this very purpose. You should be able to use the macros to create the formatting rules that you want, and achieve this behavior.

Finally, I would like to suggest that a Tuple as a key might make more sense in the resulting JSON if you make it a case class. It would certainly result in richer data in the serialized form.

For these reasons, it is my opinion that this is not an issue that should warrant a fix.