Circe Decode to sealed trait extended by multiple case classes

Question

I've seen similar questions before, but none of them have worked. I think that they ask something different so I'm asking here. I have something like this in one file:

sealed trait Thing
case class SomeThing() extends Thing
case class OtherThing() extends Thing

and in another file:

val str = //valid json
val decoded = decode[Thing](str)
println(decoded)

and I get:

Left(DecodingFailure(...))

This works if I did:

val str = //valid json
val decoded = decode[SomeThing](str)
println(decoded)

Answer 1

I had to write own encoder and decoder for serialization/deserialization.

example,

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

object CirceSubtypesSerialisers {

  def main(args: Array[String]): Unit = {

    sealed trait Data

    case class OptionsData(data: Seq[String]) extends Data
    case class TextData(data: String) extends Data

    object Data {
      implicit val decodeData: Decoder[Data] = Decoder[OptionsData].map[Data](identity).or(Decoder[TextData].map[Data](identity))

      implicit val encodeData: Encoder[Data] = Encoder.instance {
        case options @ OptionsData(_) => options.asJson
        case text @ TextData(_) => text.asJson
      }
    }

    val optionsJson ="""{ "data": ["option1", "option2"] }""".stripMargin

    decode[Data](optionsJson) match {
      case Right(r: OptionsData) => println(r)
      case Left(l) => println(l)
    }


    val textJson ="""{ "data": "hey, how can i help ya?" }""".stripMargin

    decode[Data](textJson) match {
      case Right(r: TextData) => println(r)
      case Left(l) => println(l)
    }

  }

}

output:

OptionsData(List(option1, option2))
TextData(hey, how can i help ya?)

This is also mentioned in https://circe.github.io/circe/codec.html#warnings-and-known-issues and JsonCodec for sealed traits requires an explicit object definition