Hi all! Maybe a bit similar to the previous post, ...

# serialization

[Antoine Gagnon]

Hi all!
Maybe a bit similar to the previous post, but I’m having issues understanding why the animalType field isn’t serialized in my code:

@Serializable
abstract class Animal{
    abstract val name : String
    abstract val animalType : String
}

@Serializable
class Dog(override val name:String):Animal(){
    override val animalType: String = "Dog"
}

val rex = Dog("Rex")
val string = Json.encodeToString(Dog.serializer(),rex)
println(string)

The string value at the end is always {"name":"Rex"} and doesn’t include the animalType field

[Tomasz Krakowiak]

I guess it's because animalType isn't actually a field. It's polymorphic property and Dog class implements it to always return "Dog"

[Antoine Gagnon]

My end goal is to use it to pick which serializer to use when serializing/deserializing an Animal since it’ll be a different discriminator that the default one

[Igor Brishkoski]

change val rex = Dog("") to val rex: Animal = Dog("")

[Igor Brishkoski]

And you probably don't need the Dog.serializer just Json.encodeToString(rex)

[Tomasz Krakowiak]

You can use:
kotlinx.serialization.SerialName
with custom polymorphic serializer (to change the name of "type" serial name)

@OptIn(ExperimentalSerializationApi::class)
public class AnimalSerializer<T : Any> : AbstractPolymorphicSerializer<T>() {
    public override val descriptor: SerialDescriptor =
        buildSerialDescriptor("kotlinx.serialization.Polymorphic", PolymorphicKind.OPEN) {
            element("animalType", String.serializer().descriptor)
            element(
                "value",
                buildSerialDescriptor("kotlinx.serialization.Polymorphic<${Animal::class.simpleName}>", SerialKind.CONTEXTUAL)
            )
        }.withContext(Animal::class)

    override fun toString(): String {
        return "kotlinx.serialization.AnimalSerializer"
    }
}

[Igor Brishkoski]

https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/json.md#class-discriminator You can also use this

[aleksey.tomin]

@Antoine Gagnon
You have to add @Required to animalType field.
Without this marker serialization doesn’t write into json field with default value.

[Antoine Gagnon]

Thanks @aleksey.tomin, that’s exactly what I was looking for!