So i want to deserialize a string into a `Data.Sin...

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[Stephan Schroeder]

So i want to deserialize a string into a Data.Single but it fails.

sealed class Data<T: Any> {
    class Single<T: Any>(val single: T?): Data<T>()
    class ListOf<T: Any>(val list: List<T>): Data<T>()
}

Could the reason for the mismatch be that the constructor parameter single is nullable??
The error message is: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of uk.co.whichdigital.pricingengine.Data$Single (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value (‘up and running’)
Here is my current jsonMapper config:

private val jsonMapper = ObjectMapper().apply {
        registerModule(KotlinModule())
        configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true)
        configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
    }

UPDATE: I changed the code to `Data.Single`’s generic parameter is nullable class Single<T>(val single: T): Data<T>() but the error message didn’t change.

[diesieben07]

With default configuration the representation for Single would be a JSON object:

{
  "single": <value here>
}

[diesieben07]

If you just want the value, you can use @JsonCreator on the constructor and @JsonValue on the property.

[Stephan Schroeder]

give that this is the whole TypeDefiinition class Single<T>(val single: T): Data<T>() I guess the constructor is implicit and so annotated version would be class Single<T>(@JsonValue val single: T): Data<T>()!?
The error message didn’t change. (no String-argument constructor/factory method to deserialize)

[diesieben07]

Well, you haven't annotated the constructor.
class Single<T> @JsonCreator constructor(@JsonValue val single: T) : Data<T>()

[Stephan Schroeder]

but now I did. no change 😐

[diesieben07]

let me check this...

[diesieben07]

Seems like its a problem with jackson-module-kotlin.

[diesieben07]

Without that my solution works

[Stephan Schroeder]

without the Kotlin module i’m running into problems with a data class 😕

InvalidDefinitionException: Invalid type definition for type `uk.co.whichdigital.pricingengine.GraphQlResponse`: Argument #0 has no property name, is not Injectable: can not use as Creator [constructor for uk.co.whichdigital.pricingengine.GraphQlResponse, annotations: {interface com.fasterxml.jackson.annotation.JsonCreator=@com.fasterxml.jackson.annotation.JsonCreator(mode=DEFAULT)}]

with

data class GraphQlResponse<T, D: Data<T>>@JsonCreator constructor(
    @JsonValue val data: Map<String, D>?, 
    @JsonValue val errors: List<GraphQlError>?
)

[diesieben07]

Yes, seems like you need a custom deserializer to work around this

[Stephan Schroeder]

generic custom deserialisers?? 😨

[Stephan Schroeder]

I’ll check making GraphQlResponse a normal class

[diesieben07]

It's quite simple:

class SingleDeserializer : StdConverter<String, Data.Single<String>>() {

    override fun convert(value: String?): Data.Single<String> {
        return Data.Single(value)
    }

}

@JsonDeserialize(converter = SingleDeserializer::class)
class Single<T: Any>(@JsonValue val single: T?): Data<T>()

[Stephan Schroeder]

actually the data class was fine. I had to add @JsonProperty to the fields 😮 @JsonProperty("data") val data: Map<String, D>?

[Stephan Schroeder]

The Data.Single deserialisation works without the KotlinModule.

[Stephan Schroeder]

So the simple case with String return value works now, it’d a good start! Thx 👍