Another question (everything is working, but I want to make it more foolproof. I am serializing a double-linked tree (parent references children and children reference parent, so after deserialization I have to run a function to "attach" children to the partent. Currently I just use a serialization wrapper that does it after deserialization. Is there a better way? Some time ago I asked aboud after-deserialization-hooks and there were not any. Are there any changes?

I’m getting an 

InvocationTargetException

 due to a 

NoClassDefFoundError

 when trying to invoke the serializer() method on a 

@Serializable

 class.  The class and method are found (via reflection using Ktor’s kotlinx.serialization content negotiation feature) and set accessible, but this still happens.  The annotated data class is public, but in a dependent module from the actual server that is executed. Any idea what might be wrong?

Hey I am currently stuck trying to write a custom serializer. I pretty much get a JSON that contains a list of strings. But instead of having that list of strings (which are base64 encoded strings) I would like to write a serializer that takes in the string and decodes it before saving it in the internal data class

Hi folks, there is anyway to add a new annotation and use to map primitive types. Example:

@Abs val num: Int

=>

{"num": -3}

that deserialize to 3. I already create my owns annotation for Kotlinx.serialization, I know that supports it, but was for a new Enconder of mine, not from a existing one like Json.

Is there a way with reified generics to safely get a

serializer

from a generic

T

at compile-time? I know about

KClass<T: Any>.serializer()

but that relies on reflection. Likely doesn’t exist, but it would be cool to be able to mark a generic reified argument as

@Serializable

too (maybe limited to

internal

or

private

so that the constraint could be validated at compile time) so the compiler can validate it’s not used improperly and also to allow compile-time optimization of the inlined code to get the Serializer companion/object that’s available.

Folks, I create a new Serializer for a Primitive type( String ), when I use it in the String type, works perfectly, but with List<String> does not. Its given me this exception:

Caused by: java.lang.ClassCastException: kotlin.collections.EmptyList cannot be cast to java.lang.String

How can I make my Serializer works in List and Map? My currently serializer.

@Serializer(forClass = String::class)
object ChangeColor : KSerializer<String> { ... }

Usage that is causing this exception:

@Serializable(with = ChangeColor::class)
val messages: List<String> = listOf()

Hi folks, there anyway to in a specific property usa other type of StringFormat or set at the data class? I'm trying to do something like this (code in the thread), use Json StringFormat but in a specific data class, use CSV StringFormat. But is getting exception because the compiler overrides the default

.serializer()

to this new that I created.

I've noticed though the nullables are causing an issue, do they need to be given a default value of null?

Hello, is it possible to parse JSON to data class not directly from string, but from JsonObject/JsonElement without converting it back to String and then do "parse"?

Hey everyone, I’m having some issues with my test coverage with the

patch

method generate by the @Serializable annotation. I can’t seem to figure out how to get a decoder to test it?

I'm trying to get javalin to use kotlinx.serialization instead of Jackson. I found this on their github page:

JavalinJson.toJsonMapper = object : ToJsonMapper {
     override fun map(obj: Any) =  { /* Your implementation here */ }
}

I tried this:

JavalinJson.fromJsonMapper = object : FromJsonMapper {
        override fun <T> map(json: String, targetClass: Class<T>): T {
            return Json.parse(T::class.serializer(), json)
        }
    }

But get

Unresolved reference: serializer

. Is this how to go about it?

I've got a method that fails to deserialize:

fun getAll(): Collection<User>

I get:

kotlinx.serialization.SerializationException: Can't locate argument-less serializer for class LinkedValues. For generic classes, such as lists, please provide serializer explicitly.

I think I need to somehow indicate that this method should deserialize with

User.serializer().list

. But I'm not sure how to do that.

I've got a data class with an inner LocalDate that I've annotated with

@Serializable(with = LocalDateSerializer::class)

(LocalDateSerializer is a class I've created.) However, now I'm returning a

Map<LocalDate, foo>

elsewhere and getting an error

Can't locate argument-less serializer for class LocalDate

. How do I annotate this?

Is there a way to accept Serializable types in a function? Like some supertypes or something? Usecase:

fun <T : Any> store(key: String, value: T, serializer: KSerializer<T>) {
    json.stringify(serializer, value)
}

//To, maybe reified
fun <T : SomeSuperTypeForSerializable> store(key: String, value: T) {
    json.stringify(T.serializer(), value)
}

What's the best way to get serialization to represent null values as Json

null

, instead of having the key, value pair not present (in a dict)?

It would be so great to have some way of global discovery. I now have about 70 occurences in my project of `

@Serializable(with = LocalDateSerializer::class)

Hi, I'm working on a project where null objects sometimes are being returned as [ ]. Serializer expects an object but there's an array in its place in json. Is there a way to deal with incorrect types?

To bump my previous question: Does anyone know if there's a way to apply JsonTransformingSerializer to every possible type, without specifying the type explicitly? I'm basically looking for a way to implement this, which was quite easy to do in Moshi https://pastebin.com/hmdwERm9 (snippet stolen from @jw - https://github.com/square/moshi/issues/295#issuecomment-299610834)

I have another question 😏 Using polymorphism AND generics

@Serializable
sealed class Response<T> {
    @Serializable
    data class ResponseData<T>(
        @SerialName("data")
        val data: T
    ) : Response<T>()

    @Serializable
    data class AuthData(
        @SerialName("data")
        val data: AdditionalAuthorization?
    ) : Response<AdditionalAuthorization?>()
}

I get this error

Unexpected JSON token at offset 0: Expected '[, kind: SEALED'.

It fails even with the simplest json. Apart from sealed classes I've also tried interface, open, abstract - same error, different kind given in message. Is what I'm trying to achieve supported by kotlinx.serialization?

Anyone happen to know why my serializer I've written for an enum class is failing with this

JsonDecodingException

? What is strange is that it works in certain cases, but fails in others. When I get back this response:

{
  "id": 1,
  "status": 1,
  "info": 0
}

It works fine and returns

IN_PROGRESS

. When I get this response:

{
  "id": 3,
  "status": 3,
  "info": 0
}

I encounter this error:

kotlinx.serialization.json.JsonDecodingException: Invalid JSON at 28: Expected string or non-null literal

Which is thrown from

takeString()

in

JsonReader.kt

after trying to call

decodeInt()

. If both of them were failing I would be a little less confused, but with only one of them failing I am at a loss. Is it interpreting the

3

as a byte or something, and thus failing the

TC_OTHER

and

TC_STRING

check, whereas the

1

is interpreted as a

TC_STRING

somehow? All I can think of 🤔

Hey all, I'm working with a messy REST API that requires JSON keys that change based upon table name. So a simple Json.stringify() isn't really going to work in this case. Is there a a low-level API in kotlinx.serialization.json that allows me to dynamically create JSON strings to send. (I would use a lib like klaxon, but I am using Kotlin MPP.) Any ideas?

Not sure if it is intentional but... is it necessary to add

@Serializable

to enums? I'm having issues with enums without the

@Serializable

annotation in JavaScript (haven't tested in the JVM yet)

Hi everyone, I'm getting the following error when parsing sealed classes in Kotlin/JS:

type is not registered for polymorphic serialization in the scope of class

This is my code:

@Serializable
sealed class TestClass {

    @Serializable
    @SerialName("TEST_1")
    data class TestClass1(
        val value1: String,
        val value2: Int
    ) : TestClass()

    @Serializable
    @SerialName("TEST_2")
    data class TestClass2(
        val value1: String
    ) : TestClass()

}

I found this link where the issue is discussed: https://github.com/Kotlin/kotlinx.serialization/issues/457 and seems like a fix is ready (but not yet released). I was wondering if there is a workaround that allows us to make it work until the fix is released? (I know that I can do this using a Serializer but not sure how to build it in a way that I can remove it once the fix for this is released and nothing will break).

I am making a new

Encoder

/

Decoder

and I'm confused why there is a

Encoder

and a

CompisiteEncoder

. Why does there need to be a destiction?

Is there a list of built-in serializers anywhere? I’ve looked in

commonMain

at the built-ins there, but there are some other types that the IDE isn’t complaining about, like

java.nio.Path

.

I get this error message when I annotate a class with Serializable

Cannot access 'Serializable': it is internal in '<http://kotlin.io|kotlin.io>'

I have the following problem regarding serialization of polymorphic enum classes:

interface ExampleInterface

@Serializable
enum class Example: ExampleInterface {
    TEST,
    TEST2
}


@Serializable
enum class Example2: ExampleInterface {
    WOW,
    WOW2
}

@Serializable
data class ExampleWrapper(val m: ExampleInterface)

fun main() {

    val module = SerializersModule {
        polymorphic(ExampleInterface::class) {
            Example::class with Example.serializer()
            Example2::class with Example2.serializer()
        }
    }

    val json = Json(JsonConfiguration.Stable, context = module)
    val jsonData = json.stringify(ExampleWrapper.serializer(), ExampleWrapper(Example.TEST))
    println(jsonData)
}

When I run this, the following error message is displayed:

Uncaught Kotlin exception: kotlin.IllegalStateException: Enums cannot be serialized polymorphically with 'type' parameter. You can use 'JsonConfiguration.useArrayPolymorphism' instead

Now if I do what the error message says, I will get back something like this:

{
  "m": [
    "barcodeParser.Example",
    "TEST"
  ]
}

But I would rather have it look like this:

{
  "m": "TEST"
}

How can I achieve this?

Also is there a way to automatically serialize types in Kotlin Native? It seems very hard to automatically parse primitive types to the correct Kotlin type. For example ["foo", 1, 1.0] should automatically be parsed to kotlin.String, kotlin.Int, kotlin.Float.

i’ve got a class

Foo

that i want to deserialize to null if the server gives me

{}

for the json. started to implement a

JsonTransformingSerializer

but it has a type bound

<T: Any>

which appears to mean I can’t create a `JsonTransformingSerializer<Foo?>`…I’ve worked around it for now by adding the custom serialization logic on every object that has a Foo, but that’s far from ideal