Serialize Enum as an Integer

Question

I have generated some models using the Open API tool on one of our backend APIs with Swagger. I got the following as the enum definition:

@Serializable
enum class ClientBackgroundState(val value: kotlin.Int) {

    @SerialName(value = "0")
    NONE(0),

    @SerialName(value = "1")
    FOREGROUND(1),

    @SerialName(value = "2")
    BACKGROUND(2);
}

When I use Kotlin Serializer, it serializes the above type into a String like "FOREGROUND" and the Backend API explodes because it wants an Integer.

Is there a way to configure the serializer to convert this enum to an Integer?

Answer 1

I have this solution. Create a "simple" base class:

open class EnumAsIntSerializer<T:Enum<*>>(
    serialName: String,
    val serialize: (v: T) -> Int,
    val deserialize: (v: Int) -> T
) : KSerializer<T> {
    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor(serialName, PrimitiveKind.INT)

    override fun serialize(encoder: Encoder, value: T) {
        encoder.encodeInt(serialize(value))
    }

    override fun deserialize(decoder: Decoder): T {
        val v = decoder.decodeInt()
        return deserialize(v)
    }
}

And use it this way per an enum type:

private class PartOfSpeechSerializer: EnumAsIntSerializer<PartOfSpeech>(
    "PartOfSpeech",
    { it.value },
    { v -> PartOfSpeech.values().first { it.value == v } }
)

@Serializable(with = PartOfSpeechSerializer::class)
enum class PartOfSpeech(val value: Int) {
    Undefined(0),
    Noun(1),
    Verb(2),
    Adjective(3),
    Adverb(4),
    Pronoun(5),
    Preposition(6),
    Conjunction(7),
    Interjection(8)
}