Hi! I am trying to use `JsonContentPolymorphicSeri...

# serialization

[Didier Villevalois]

Hi! I am trying to use JsonContentPolymorphicSerializer to manually select what de-serializer to use for my polymorphic class hierarchies, while using JsonTransformingSerializer to remove the type fields at serialization.

I am doing this:

inline fun <reified T : Any> noDiscriminatorPolymorphic(crossinline serializerSelector: (element: JsonElement) -> DeserializationStrategy<out T>): KSerializer<T> {
    val serializer = object : JsonContentPolymorphicSerializer<T>(T::class) {
        override fun selectDeserializer(element: JsonElement): DeserializationStrategy<out T> {
            return serializerSelector(element)
        }
    }
    return NoDiscriminantSerializer(serializer)
}

class NoDiscriminantSerializer<T : Any>(serializer: KSerializer<T>) :
    JsonTransformingSerializer<T>(serializer) {
    override fun transformSerialize(element: JsonElement): JsonElement {
        val content =
            element.jsonObject.mapValues { (_, v) -> if (v is JsonObject) JsonObject(v.jsonObject - "type") else v } - "type"
        return super.transformSerialize(JsonObject(content))
    }
}

and then this:

val myFormat = Json {
    serializersModule = SerializersModule {
        contextual(noDiscriminatorPolymorphic { element ->
            when {
                "thisField" in element.jsonObject -> ThisClass.serializer()
                "thatField" in element.jsonObject -> ThatClass.serializer()
                else -> error("Unknown subclass")
            }
        })
    }
}

But the type fields are always serialized. Does anyone know what I am missing?

[Emil Kantis]

Is the supertype of ThisClass and ThatClass marked as @Serializable perhaps?

[Didier Villevalois]

Yes, indeed. Thank you @Emil Kantis, that was the tip I needed!
I removed the @Serializable annotation from the supertype, annotated its uses in other @Serializable with @Contextual and all rolled as expected. Thank you!

[Emil Kantis]

You're welcome 🙂