json.scala

object Model {
  
  trait Mutation[A]{
    val doc: A
  }

  case class Upsert[A](doc: A) extends Mutation[A]
  case class Delete[A](doc: A) extends Mutation[A]
  
  // Json format
import play.api.libs.functional.syntax._
  
class MutationFormat[A] extends Format[Mutation[A]] {
  def writes(o: Mutation[A]) = Json.obj(
    "kind" -> o match {
      case _: Upsert[_] => "upsert"
      case _: Delete[_] => "delete"
    },
    "doc" -> Json.toJson(o.doc)
  )

  def reads(js: JsValue) = {
  (
    (__ \ "kind").reads[String] ~
    (__ \ "doc").reads[A]
  ).validate(js)
    // Return JsResult (either JsSuccess or JsError)
  }
}