Hi! I apologize if this has been asked before, but...

# ktor

[sonofblip]

Hi! I apologize if this has been asked before, but is there a good canonical way in ktor to map query params from a GET request to a model class in kotlin? Here’s an example:

application.routing {
    get("myroute") {
        val queryParams = call.parameters // the query params from the call
        val paramsMap: Map<String, String> = queryParams.toMap().mapValues { it.value.first() } // I can put them in a map of string fairly easily
        val instanceOfMyClass: MyClass = MyClass(paramsMap["val1"], paramsMap["val2"], etc...) // I have to map them to my class manually each time :(
        // do stuff with the query params
        call.respondJson("your response here.")
    }
}

To be clear, the equivalent of what I’m looking for in spring would look like:

import javax.validation.Valid;

@RequestMapping(value = "/getItem", method = RequestMethod.GET)
public ServiceRequest<List<SomeModel>> getClaimStatuses(@Valid RequestParamsModel model) {
    // ...
}

and in JAX-RS it’d use @BeanParam https://dennis-xlc.gitbooks.io/restful-java-with-jax-rs-2-0-2rd-edition/en/part1/chapter5/bean_param.html

[Dennis Schröder]

Yes there is! I`ll look it up for you. Just a second.

[Dennis Schröder]

val myDataClass = call.receive<MyDataClass>()

The feature you are looking for, when I get you right, is the Content Negotiation Feature.

https://ktor.io/servers/features/content-negotiation.html

[sonofblip]

does that work with query parameters? I’m only finding examples of using it to receive request bodies

[sonofblip]

and when I do it in my get request it throws CannotTransformContentToTypeException. Even with all the values of the class’ constructor (including the nullable ones) passed in.

[tseisel]

Take a look at the Locations feature : https://ktor.io/servers/features/locations.html

[halley]

I had done something with objectMapper.convertValue(map, class) in the past, but that was in a different life and I don’t have that code anymore.

[Kevin Schmeichel]

It's pretty easy to do using gson

[Kevin Schmeichel]

https://stackoverflow.com/questions/49860916/how-to-convert-a-kotlin-data-class-object-to-map

[Kevin Schmeichel]

But, as far as I know, this is the only reason to use Locations instead of Routing

[sonofblip]

yeah the Locations feature worked like a charm! Only downside is that it doesn’t allow for multiple different models to be combined in one route

[sonofblip]

but it works for what I need, and you can always write a wrapper class to abstract if you need to

[Kevin Schmeichel]

another downside, in my opinion, is that Locations removes the path from the routing definition, and you have to keep jumping back to the annotation to view the path

[Kevin Schmeichel]

no idea why path data isn't parsed just like body data, with something similar to call.receive<>()