Sealed trait member with own codec

[shmishleniy]

Hi,

import com.github.plokhotnyuk.jsoniter_scala.core._
import com.github.plokhotnyuk.jsoniter_scala.macros._
import org.scalatest.funspec.AnyFunSpec
import org.scalatest.matchers.should.Matchers

sealed trait BatchSource
case class Mother(tag: String) extends BatchSource
case class Package(id: String, tag: String) extends BatchSource

class CodecSpec extends AnyFunSpec  {
  implicit val codecMother: JsonValueCodec[Mother] = JsonCodecMaker.make[Mother](CodecMakerConfig.withDiscriminatorFieldName(Some("source")).withFieldNameMapper{
    case "tag" => "tag_id"
  })
  implicit val codecPackage: JsonValueCodec[Package] = JsonCodecMaker.make[Package](CodecMakerConfig.withDiscriminatorFieldName(Some("source")).withFieldNameMapper{
    case "tag" => "tag_id"
  })
  implicit val codecBatchSource: JsonValueCodec[BatchSource] = JsonCodecMaker.make[BatchSource](CodecMakerConfig.withDiscriminatorFieldName(Some("source")))

  it("codec") {
    val b = Package(id="17ebf4294-59ca-45a9-a6b7-373c2aa890fa", tag="ASDZXC123123")
    assert(writeToString[Package](b)     === """{"id":"17ebf4294-59ca-45a9-a6b7-373c2aa890fa","tag_id":"ASDZXC123123"}""")
    assert(writeToString[BatchSource](b) === """"{source":"Package","id":"17ebf4294-59ca-45a9-a6b7-373c2aa890fa","tag_id":"ASDZXC123123"}""")
  }
}

in case we encode by trait writeToString[BatchSource]
expected:
{source":"Package","id":"17ebf4294-59ca-45a9-a6b7-373c2aa890fa","tag_id":"ASDZXC123123"}
actual:
{"id":"17ebf4294-59ca-45a9-a6b7-373c2aa890fa","tag_id":"ASDZXC123123"}

seem trait codec codecBatchSource just using codecPackage without discriminator field.

as you can see I explicitly tried .withDiscriminatorFieldName(Some("source")) in codecPackage

[plokhotnyuk]

Hi, Andrii!

Thanks for trying and raising a question.

As for me, derivation of codecs works quite logically - if you want to store a product type (not a sum type or an enum) then the discriminator (or a type tag) is redundant.

The problem here that implicit values for codecMother and codecPackage are not isolated in the separated scope and override derivation of codecs for corresponding types in the JsonCodecMaker.make[BatchSource] call.

Below is an example of how derivation and declaration of implicit values can be isolated to meet your expectations:

object Codecs {
  val codecBatchSource: JsonValueCodec[BatchSource] = JsonCodecMaker.make[BatchSource](CodecMakerConfig.withDiscriminatorFieldName(Some("source")).withFieldNameMapper{
    case "tag" => "tag_id"
  })
  val codecPackage: JsonValueCodec[Package] = JsonCodecMaker.make[Package](CodecMakerConfig.withDiscriminatorFieldName(Some("source")).withFieldNameMapper{
    case "tag" => "tag_id"
  })
}

object ImplicitCodecs {
  implicit val codecBatchSource: JsonValueCodec[BatchSource] = Codecs.codecBatchSource
  implicit val codecPackage: JsonValueCodec[Package] = Codecs.codecPackage
}
  
import ImplicitCodecs._

[shmishleniy]

So in case I need tag field mapping only for package but not for mother I should provide custom codec for sealed trait