graphQL query return type does not support custom generic.

Library Version com.expediagroup:graphql-kotlin-spring-server:2.0.0-RC6

Describe the bug i am running a graphQL server. this is my test code

import com.expediagroup.graphql.hooks.SchemaGeneratorHooks
import com.expediagroup.graphql.spring.operations.Query
import graphql.Scalars
import graphql.schema.GraphQLInputObjectField
import graphql.schema.GraphQLInputObjectType
import graphql.schema.GraphQLType
import org.springframework.stereotype.Component
import kotlin.reflect.KType

@Component
class GenericQuery : Query {

    fun getWidgetValue(widget: Widget<Long>): Long {
        return widget.value
    }

}

data class Widget<T>(val value: T)

@Component
class CustomSchemaGeneratorHooks : SchemaGeneratorHooks {

    override fun willGenerateGraphQLType(type: KType): GraphQLType? = when (type.classifier) {
        Widget::class -> createWidgetGraphQLType(type)
        else -> null
    }

    fun createWidgetGraphQLType(type: KType): GraphQLType {
        return GraphQLInputObjectType
            .newInputObject()
            .name("WidgetInput")
            .field(
                GraphQLInputObjectField.newInputObjectField()
                    .name("value")
                    .type(Scalars.GraphQLString)
                    .build()
            ).build()
    }

}

To Reproduce when i query

query {
    getWidgetValue(
        widget: {
            value: "foo"
        }
    )
}

i got error info:

java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl cannot be cast to java.lang.Class
  at com.expediagroup.graphql.generator.extensions.KParameterExtensionsKt.javaTypeClass(kParameterExtensions.kt:43) ~[graphql-kotlin-schema-generator-2.0.0-RC6.jar:2.0.0-RC6]

Expected behavior i wanna graphQL server return result:

{
  "widget": {
           "value": "1" // string format
   }
}

i am read source code, i think error in kParameterExtensions.kt on 43 line.

i try to fix. it is my demo code.

internal fun KParameter.javaTypeClass(): Class<*> = 

    if (this.isList()) { 
         this.type.getKClass().java  

    } else { 

        val javaType = type.javaType 

        if(javaType is ParameterizedType) { 

            javaType.rawType as Class<*> 

        } else { 

            javaType as Class<*> 

        }  

    } 

point is generic is myself defined. and i expect specific return value. but just can not cast to target.

[dariuszkuc]

@Ncaffeine again the underlying problem is that while Kotlin supports generics and you can definitely code whatever, generics currently cannot be represented in GraphQL schema so your Kotlin data model CANNOT be mapped 1:1 to a schema.

[oooplz]

@Ncaffeine再次提出了潜在的问题，尽管Kotlin支持泛型并且您绝对可以编写任何代码，但泛型当前无法在GraphQL模式中表示，因此您的Kotlin数据模型无法以1：1映射到模式。

thank you.