json deserialize of ListBuffer[(String,String)] in play framework

Question

i am developing app using play framework in scala i want response in json but how to do that compile time error is coming

 No Json deserializer found for type List[(String, String)]. Try to implement an implicit Writes or Format for this type.

List buffer is

ListBuffer((This,a choke), (a Cv,15.6 gal))

i also did this

Json.toJson(list))

but still getting error.

any one give me some idea to solve this issue.

Answer 1

What json representation of (String, String) do you expect it to be? If it is something like this:

yourListName : {
  "1" : "2",
  "3" : "4"
}

then you could just use Json.toJson(list.toMap). Otherwise, you must define a Writes for a (String, String) like this:

implicit val writer = new Writes[(String, String)] {
    def writes(c: (String, String)): JsValue = {
      Json.obj("something" -> c._1 + ", " + c._2)
      //or like this:
      //Json.obj(c._1 -> c._2)
    }
  }

Be sure to have this writer in scope

Answer 2

As discussed in this thread [2.1] Json.format macros and Tuple2 play-json 2.1 doesn't support tuples yet mainly because json doesn't support tuples. If you want your tuples to be writtern as an array you might use implicit format for tuples:

implicit def tuple2Writes[A, B](implicit aWrites: Writes[A], bWrites: Writes[B]): Writes[Tuple2[A, B]] = new Writes[Tuple2[A, B]] {
  def writes(tuple: Tuple2[A, B]) = JsArray(Seq(aWrites.writes(tuple._1), bWrites.writes(tuple._2)))
}

Answer 3

You can do this in a line, simply declare this implicit:

implicit def tuple2[A : Writes, B : Writes] = Writes[(A, B)] ( t =>  Json.obj("something1" -> t._1, "something1" -> t._2) )