scala play reads parse nested json

Question

I'm using implicit val reads to map Json like:

{
   "id": 1
   "friends": [
    {
      "id": 1,
      "since": ...
    },
    {
      "id": 2,
      "since": ...
    },
    {
      "id": 3,
      "since": ...
    }
  ]
}

to a case class

case class Response(id: Long, friend_ids: Seq[Long])

I can only make it work with an intermediate class that reflects the JSON friends structure. But I never use it in my app. Is there a way to write a Reads[Response] object so that my Response class would map directly to the JSON given?

Answer 1

You only need simple Reads[Response] with explicit Reads.seq() for friend_ids such as

val r: Reads[Response] = (
  (__ \ "id").read[Long] and
    (__ \ "friends").read[Seq[Long]](Reads.seq((__ \ "id").read[Long]))
  )(Response.apply _)

and result will be:

r.reads(json)

scala> res2: play.api.libs.json.JsResult[Response] = JsSuccess(Response(1,List(1, 2, 3)),)