Hello! I am trying to deserialize a json element that ca be a single object or an empty array when no address returned. "Address":{"firstName":"firstNameValue"} or "Address":[] What I did this was to use

JsonTransformingSerializer.transformDeserialize()

and return a null JsonElement if the element is an array. And since the

JsonTransformingSerializer

does not currently support nullable types I created a

NullableJsonTransformingSerializer

. I was wondering if there is another way to deserialize the Address, and not use the transformDeserialize().

I think that

JsonTransformingSerializer

supports decoding as null - but you have to return the

JsonNull

object, instead of a literal

null

Thank you @Adam S for your suggestion! Looks like is throwing an exception

Exception in thread "main" kotlinx.serialization.json.internal.JsonDecodingException: Expected class kotlinx.serialization.json.JsonObject as the serialized body of com.stockx.stockx.sell.checkout.ui.Address, but had class kotlinx.serialization.json.JsonNull

so I tried specifying the serializer as nullable but I get a compile error

hmm, yeah so you were right,

JsonTransformingSerializer

isn’t suitable. What you could do is decode

address

to

JsonElement

, and in code convert it to

Address

if it’s a

JsonObject

@Serializable
data class Project(
  @SerialName("address")
  private val _address: JsonElement
) {
  val address: Address? get() = when (_address) {
    is JsonObject -> Json.decodeFromJsonElement(_address)
    else          -> null
  }
}

I like this way, because there’s no custom serializer - it’s just plain Kotlin code. It’s a little weird and verbose though, and the automatic

toString()

doesn’t look correct You could automate it a little by creating a value class that will wrap the logic. Value classes are nice because they’re ‘transparent’ in terms of the actual content, but you can still use them to inject logic into Kotlinx Serialization

@Serializable
data class Project(
  private val address: AddressWrapper
)

@Serializable
data class Address(val firstName: String)

@JvmInline
@Serializable
value class AddressWrapper(private val value: JsonElement) {
  val address: Address? get() = when (value) {
    is JsonObject -> Json.decodeFromJsonElement(value)
    else          -> null
  }

  override fun toString() = address.toString()
}

This is cool! 🤩 Agree that is more transparent and it's great that no custom serializer is needed. Thanks a lot for your help, I really appreciate it!

my pleasure!