Scala object to Json with Play API - json

Question

I need to handle a case that hasn't been answered by this question: Convert any Scala object to JSON
Basically, I don't know how to handle List and Map types. I've tried the following which doesn't work:
implicit val anyValWriter = Writes[Any] (a =>
a match {
case v: Double => Json.toJson(v)
case v: Float => Json.toJson(v)
case v: Long => Json.toJson(v)
case v: Int => Json.toJson(v)
case v: String => Json.toJson(v)
case v: Iterable[Any] => Json.toJson(v.map(t => Json.toJson(t)).toList)
case v: Map[String, Any] => JsObject(v.map { case (k, v) => (k, Json.toJson(v)) }.toList)
// or, if you don't care about the value
case _ => throw new RuntimeException("Type not serializable.")
})
The resulting error is: No Json serializer found for type Any. Try to implement an implicit Writes or Format for this type.
Trying to add anyValWriter to Json.toJson results in: recursive value anyValWriter needs type
Any idea?

Answer 1

I finally sorted my problem out through a workaround. I've chosen not to handle Iterable & Map types in the Writes[Any] and I used a wrapper to handle both types as in my case Any won't be an occurrence of either List[...] or Map[String, Any].
Here's the code for those who are interested:
implicit val anyValWriter = Writes[Any] (a =>
a match {
case v: Double => Json.toJson(v)
case v: Float => Json.toJson(v)
case v: Long => Json.toJson(v)
case v: Int => Json.toJson(v)
case v: String => Json.toJson(v)
case v: JsArray => v
// or, if you don't care about the value
case _ => throw new RuntimeException("Type not serializable.")
})
And the wrapper:
def convertToJsonValue(v : Iterable[Map[String, Any]])(implicit write: Writes[Any]) = {
JsArray(v.map(t => JsObject(t.map {
case (k, value) => (k, Json.toJson(value)(write)) }.toList)).toList)
}
I'll find out later if I can sort out the ugly JsArray case.
PS: I know it's wrong but I'm using a SQL API which returns Map[String, Any] as I don't know the columns that will be returned (and I have good reasons for this and to not use the ORM feature).