How to convert generic potentially nested map Map[String, Any] to case class using any library in Scala?

Question

I've not had much joy with reflection, this answer using shapeless works for some cases (but seems to have many edge cases) Shapeless code to convert Map[String, Any] to case class cannot handle optional substructures

Does anyone know of a nice library that does this in just a few LOCs?

Answer 1

We can use circe

import io.circe._
import io.circe.generic.auto._
import io.circe.parser._
import io.circe.syntax._


def mapToJson(map: Map[String, Any]): Json =
    map.mapValues(anyToJson).asJson

  def anyToJson(any: Any): Json = any match {
    case n: Int => n.asJson
    case n: Long => n.asJson
    case n: Double => n.asJson
    case s: String => s.asJson
    case true => true.asJson
    case false => false.asJson
    case null | None => None.asJson
    case list: List[_] => list.map(anyToJson).asJson
    case list: Vector[_] => list.map(anyToJson).asJson
    case Some(any) => anyToJson(any)
    case map: Map[String, Any] => mapToJson(map)
  }

def mapToCaseClass[T : Decoder](map: Map[String, Any]): T = mapToJson(map).as[T].right.get

Then, if we have any types that are not primitive, we just need to add these to our anyToJson along with an encoder/decoder pair that can encode/decode this type as something primitive.

E.g. we can represent java.sql.Timestamp with Long, then

import cats.syntax.either._

  import io.circe.Decoder
  import io.circe.Encoder

  implicit val decodeTimestamp: Decoder[Timestamp] = Decoder.decodeLong.emap(long =>
    Either.catchNonFatal(new Timestamp(long)).leftMap(_ => "Timestamp")
  )

implicit val encodeTimestamp: Encoder[Timestamp] = Encoder.encodeLong.contramap[Timestamp](_.getTime)

and we need to add the line to anyToJson

case n: Timestamp => n.asJson