Implicit JsonWriter for trait not working - scala

Question

I have class as below
trait RiskCheckStatusCode {
def code: String
def isSuccess: Boolean
}
object RiskCheckStatusCode {
val SUCCESS = SuccessRiskCheckStatusCode("1.1.1")
val FAIL = FailRiskCheckStatusCode("2.2.2")
case class SuccessRiskCheckStatusCode(code: String) extends RiskCheckStatusCode {
override def isSuccess = true
}
object SuccessRiskCheckStatusCode {
import spray.json.DefaultJsonProtocol._
implicit val formatter = jsonFormat1(SuccessRiskCheckStatusCode.apply)
}
case class FailRiskCheckStatusCode(code: String) extends RiskCheckStatusCode {
override def isSuccess = false
}
object FailRiskCheckStatusCode {
import spray.json.DefaultJsonProtocol._
implicit val formatter = jsonFormat1(FailRiskCheckStatusCode.apply)
}
}
and now I would like to convert the list of RiskCheckStatusCode to json
object Main extends App{
import spray.json._
import spray.json.DefaultJsonProtocol._
val l = List(RiskCheckStatusCode.SUCCESS, RiskCheckStatusCode.FAIL)
implicit object RiskCheckStatusCodeJsonFormat extends JsonWriter[RiskCheckStatusCode] {
override def write(obj: RiskCheckStatusCode): JsValue = obj match {
case obj: SuccessRiskCheckStatusCode => obj.toJson
case obj: FailRiskCheckStatusCode => obj.toJson
}
}
def json[T](list: T)(implicit formatter: JsonWriter[T]) = {
print(list.toJson)
}
json(l)
}
but the json method can not find jsonWriter[RiskCheckStatusCode].
Can you explain why? Maybe should I do it differently for trait type?
Edit:
It works for
val l: RiskCheckStatusCode = RiskCheckStatusCode.SUCCESS
so the problem is with List[RiskCheckStatusCode] because I have a formatter for RiskCheckStatusCode, not for List[RiskCheckStatusCode]. I tried import DefaultJsonProtocol but it still does not work.
import spray.json.DefaultJsonProtocol._
I have to change the definitions? From
implicit object RiskCheckStatusCodeJsonFormat extends JsonWriter[RiskCheckStatusCode]
to
implicit object RiskCheckStatusCodeJsonFormat extends JsonWriter[List[RiskCheckStatusCode]]
error:
Error:(28, 7) Cannot find JsonWriter or JsonFormat type class for List[com.example.status.RiskCheckStatusCode]
json(l)
Error:(28, 7) not enough arguments for method json: (implicit formatter: spray.json.JsonWriter[List[com.example.status.RiskCheckStatusCode]])Unit.
Unspecified value parameter formatter.
json(l)

Answer 1

Your code is fine you are just not having toJson in your scope (it is located in the package object of spray.json).
Add it and your code should compile:
object Main extends App with DefaultJsonProtocol {
import spray.json._
// ...
}
Furthermore spray has some issues to lift JsonWriter through derived formats (see this for details).
You can switch to JsonFormat instead:
implicit object RiskCheckStatusCodeJsonFormat extends JsonFormat[RiskCheckStatusCode] {
override def write(obj: RiskCheckStatusCode): JsValue = obj match {
case obj: SuccessRiskCheckStatusCode => obj.toJson
case obj: FailRiskCheckStatusCode => obj.toJson
}
override def read(json: JsValue): RiskCheckStatusCode = ???
}
In addition, to cleanup the type of your List change the definition of RiskCheckStatusCode to (this explains more details):
sealed trait RiskCheckStatusCode extends Serializable with Product