Support Map<K, V> as input argument type

[andreyTheGreatest]

Is your feature request related to a problem? Please describe.
I have an input argument of Map<K, V> type for a subscription request. I map it to ExtendedScalars.JSON to avoid TypeNotSupportedException, however with a 6.x version of generator package I am getting PrimaryConstructorNotFound: Invalid input object Map - missing public primary constructor.
I have noticed related discussions about this problem in #1518 and #1520. But they suggest to create either a constructor, because of predefined POJO java classes usage, or a custom FunctionDataFetcher . Any Map implementation doesn't provide one constructor only, and creating custom support of a simple Map via FunctionDataFetcher seems like an overkill to me.

Describe the solution you'd like
I'd suggest Map support is as crucial as List support as an input argument. As far as I am concerned, List doesn't generate PrimaryConstructorNotFound, so maybe a similar behavior could be provided for the Map as well.

[smyrick]

Maps are not supported per the GraphQL spec, however you should be able to use ExtendedScalars.JSON by setting up your schema generator hooks to include the Map type as a valid type, map that to JSON and include extended scalars in your package config

#1198

[andreyTheGreatest]

Thanks for the answer!
I have it already set up, as suggested.

fun schemaGeneratorHooks() = object : SchemaGeneratorHooks {
    override fun willGenerateGraphQLType(type: KType): GraphQLType?  = when (type.classifier) {
        Map::class -> ExtendedScalars.Json
        else -> null
    }
}

graphqlSchema = toSchema(
    config = SchemaGeneratorConfig(
    supportedPackages = listOf("graphql.scalars.ExtendedScalars", ...),
        hooks = schemaGeneratorHooks(),
    ),
    ...
)

It works flawlessly with Map as an output type. The problem emerges, when I am using Map as an input type. The exception that is thrown: PrimaryConstructorNotFound: Invalid input object Map - missing public primary constructor. I have tried swapping Map with HashMap or LinkedHashMap, however, these implementations include multiple constructors, thus MultipleConstructorsFound is thrown. This suggests implementing Map with one constructor.

When I downgrade to 5.x version, input Map type works as well. From my understanding, this is due to drop of Jackson support mentioned here. Although, the Map isn't supported per GraphQL spec, with the previous version of this lib everything worked as expected, whereas with the new one I have to provide custom FunctionDataFetcher or create a custom implementation of Map. I understand why it is so for the POJO classes, but Map is widely used.

If this is the expected behavior, however, and my arguments don't suffice, then I will opt out of my take and apply one of the previously mentioned approaches (it just doesn't feel right to write custom Map implementation just for the sake of providing single constructor only ;) ).

[smyrick]

Tagging the maintainer for visibility, @samuelAndalon and @tapaderster

[samuelAndalon]

@andreyTheGreatest could you share a repo link with minimal setup to reproduce the error ? -- you can use spring boot starter and include graphql-kotlin-server.

[dariuszkuc]

IMHO this issue should be closed in favor of #1445 which tackles this more generically. TLDR we should provide a mechanism for easily supporting additional input types - right now folks have to write their own data fetcher that duplicates the default logic.

[dariuszkuc]

We will not be supporting generic Map<K, V> as input arguments (as GraphQL specification does not support maps). Closing this in favor of providing mechanism to easily modify the default data fetchers to include custom logic (see #1445).

--- edit ---
if your custom scalars are top level args (i.e. not nested within some objects) you could also just extend the provided data fetchers and provide your custom logic in mapParameterToValue (similar to what SpringDataFetcher does over the default FunctionDataFetcher)