How can I register multiple serializers when using...

# ktor

[Lawik]

How can I register multiple serializers when using a class with generic type, for example:

Response<Foo>
Response<Bar>

[ribesg]

You can’t have multiple serializers for one type. Do you have custom serializers? Your example requires 3 serializers: one for Response, one for Foo and one for Bar. If all 3 have the @Serializable annotation it should just work.

[Lawik]

All 3 have the @Serializable annotation.

[Lawik]

this is my current code

private val client = HttpClient {
        install(JsonFeature) {
            serializer = KotlinxSerializer().apply {
                register(Response.serializer(FooDTO.serializer()))
                register(Response.serializer(PersonDTO.serializer()))
            }
        }
    }

Sadly, this causes `PersonDTO`'s serializer to apply for both PersonDTO and FooDTO.

[Lawik]

This is my Response class

@Serializable
data class Response<T>(val code: Int, val body: T?)

[ribesg]

You should not need to register anything

[ribesg]

If you have @Serializable on all 3 models it just works (In a JVM context)

[Lawik]

I'm working on JS at the moment, this is what I get when I don't register anything:

"Fatal exception in coroutines machinery for CancellableContinuation(DispatchedContinuation[WindowDispatcher@1, [object Object]]){[object Response]}@2. Please read KDoc to 'handleFatalException' method and report this incident to maintainers; caused by ReceivePipelineException: Fail to run receive pipeline: NoTransformationFoundException: No transformation found: class JsHttpResponse -> class Response"

[ribesg]

Ok, then if you’re not on the JVM you need to set all mappers manually for each class as reflection doesn’t work

[ribesg]

I use setMapper(MyDataClass::class, MyDataClass.serializer())

[ribesg]

But I think you can’t deserialize generics? I don’t use JS so I’m not sure. You can’t deserialize generics in native

[Lawik]

That brings me back to my original question, how can one do this when your class has a type parameter, the last setMapper/register overwrites the previous one of the same class 😅

[ribesg]

You can’t

[ribesg]

Why don’t you just return Foo?

[Lawik]

I want to put http info in the response class, status code, headers, etc.

[ribesg]

Ok, that’s why you want a generic. Are you sure you’re going to use all that?

[ribesg]

I just return the model

[Lawik]

I probably will at some point, I intend to add more data to the Response class, error message(s) for instance.

[ribesg]

Ok, but why? Why would you have error messages in there?

[Lawik]

Where would you put them?

[ribesg]

You can have a Feature which catches non-2xx status codes and throws an exception

[ribesg]

If you have a standard error message object, then you can deserialize the body as an ErrorBody or something in this Feature

[ribesg]

I’m not sure about an API returning error messages which should be displayed to the user though, feels weird

[Lawik]

Thanks, I'll try it out later tonight, if not, on Monday.