Question: can you have a value class that serializes like a data class? I got bit by making a value ...

# serialization

[chiroptical]

Question: can you have a value class that serializes like a data class? I got bit by making a value class over a single field JSON payload.

[chiroptical]

Basically fighting with UUIDs serialization to/from json and to the database. ignore this. I am confusing two of my issues ha

[Emil Kantis]

I think you'd need a JsonTransformingSerializer for that.

inline fun <reified T : Any> objectWrappingSerializer(fieldName: String) = object : JsonTransformingSerializer<T>(serializer()) {
   override fun transformSerialize(element: JsonElement): JsonElement {
      return buildJsonObject {
         put(fieldName, element)
      }
   }

   override fun transformDeserialize(element: JsonElement): JsonElement {
      return element.jsonObject[fieldName]!!
   }
}

create your serializer like:

object MyValueClassSerializer :KSerializer<MyValueClass> by objectWrappingSerializer("fieldName") 

@Serializable(with = MyValueClassSerializer::class)
value class MyValueClass(..)

[chr]

☝️ this doesn't seem to work for me, since it looks like the serializer() we're trying to reference in the argument is the serializer that we're trying to construct in objectWrappingSerializer(...)

[Emil Kantis]

Sorry, you're right. The usage is wrong but the objectWrpapingSerializer works..

[Emil Kantis]

@Serializable
@JvmInline
private value class PersonName(val value: String)
object PersonNameSerializer : KSerializer<PersonName> by objectWrappingSerializer("name")

class ObjectWrappingSerializerTest : FreeSpec(
   {
      "Serializes correctly" {
         Json.encodeToString(PersonNameSerializer, PersonName("John")) shouldEqualJson """{"name":"John"}"""
      }
   },
)

Passes now that we're creating the auto-generated serializer first