I m trying to return a class that extends graphql relay Conn

Question

I m trying to return a class that extends graphql relay Connection class in a Query function as shown in the snippet below ```import com androidmaestro users data repository UserRepository import com androidmaestro users domain entity UserEntity import com expediagroup graphql types operations Query import graphql relay class UsersQuery private val repository UserRepository Query suspend fun users first Int cursor String UsersConnection = repository getAll first cursor class UsersConnection users List lt Edge lt UserEntity gt gt userPageInfo DefaultPageInfo DefaultConnection lt UserEntity gt users userPageInfo ``` However the schema generation fails with the error shown below ``` Caused by java lang IllegalArgumentException Class declares 1 type parameters but 0 were provided at kotlin reflect full KClassifiers createType KClassifiers kt 53 at kotlin reflect full KClassifiers createType$default KClassifiers kt 45 at com expediagroup graphql generator internal types GenerateObjectKt generateObject generateObject kt 46 at com expediagroup graphql generator internal types GenerateGraphQLTypeKt getGraphQLType generateGraphQLType kt 74 at com expediagroup graphql generator internal types GenerateGraphQLTypeKt access$getGraphQLType generateGraphQLType kt 1 at com expediagroup graphql generator internal types GenerateGraphQLTypeKt$objectFromReflection$1 invoke generateGraphQLType kt 63 at com expediagroup graphql generator internal types GenerateGraphQLTypeKt$objectFromReflection$1 invoke generateGraphQLType kt at com expediagroup graphql generator internal state TypesCache buildIfNotUnderConstruction$graphql kotlin schema generator TypesCache kt 108 at com expediagroup graphql generator internal types GenerateGraphQLTypeKt objectFromReflection generateGraphQLType kt 62 at com expediagroup graphql generator internal types GenerateGraphQLTypeKt generateGraphQLType generateGraphQLType kt 40 at com expediagroup graphql generator internal types GenerateGraphQLTypeKt generateGraphQLType$default generateGraphQLType kt 36 at com expediagroup graphql generator internal types GenerateFunctionKt generateFunction generateFunction kt 54 at com expediagroup graphql generator internal types GenerateFunctionKt generateFunction$default generateFunction kt 33 at com expediagroup graphql generator internal types GenerateQueryKt generateQueries generateQuery kt 43 at com expediagroup graphql generator SchemaGenerator generateSchema SchemaGenerator kt 80 at com expediagroup graphql generator SchemaGenerator generateSchema$default SchemaGenerator kt 73 at com expediagroup graphql generator ToSchemaKt toSchema toSchema kt 41 at com expediagroup graphql generator ToSchemaKt toSchema$default toSchema kt 37 at com androidmaestro graphql Schema lt clinit gt Schema kt 51 76 common frames omitted 2021 03 23 14 01 21 087 eventLoopGroupProxy 4 1 ERROR Application Unhandled exception java lang NoClassDefFoundError Could not initialize class com androidmaestro graphql Schema```

Shane Myrick · Answer

It is the same issue as this <https kotlinlang slack com archives CQLNT7B29 p1616235196005400> With the changes in 4 0 0 to support default arguments nullable arguments must have a default as the client may not pass in a value You can think of it in terms of calling the Kotlin function too What do we do if someone doesn t provide a value for a GraphQL optional arg

Jabez Magomere · Answer

< Shane Myrick> thank you for the detailed explanation i ve made a change to the nullable query parameter and i have assigned it a default null value however i still get the same exception the return type of the query is a class with a generic superclass DefaultConnection lt T gt from graphql relay might the error be related to the lack of generic support ```import com androidmaestro users data repository UserRepository import com androidmaestro users domain entity UserEntity import com expediagroup graphql types operations Query import graphql relay class UsersQuery private val repository UserRepository Query suspend fun users first Int cursor String = null UsersConnection = repository getAll first cursor class UsersConnection users List lt Edge lt UserEntity gt gt userPageInfo DefaultPageInfo DefaultConnection lt UserEntity gt users userPageInfo ``` DefaultConnection snippet ``` A default implementation of link graphql relay Connection PublicApi public class DefaultConnection lt T gt implements Connection lt T gt ```

Shane Myrick · Answer

Yep we cannot support generics as GraphQL as no concept of generics in the type system either You could create a custom scalar to be some generic object but then you are loosing the benefits of actually having a strongly typed API

Jabez Magomere · Answer

True thank you for the much needed help any ideas or samples on implementing cursor based pagination with graphql kotlin I initially thought of using the relay spec the classes already exist in the graphql java package but since generics are not supported i have to find a cleaner alternative to custom scalars

Shane Myrick · Answer

If you are implementing these classes we can still support the `Connection` wrappers You just need to make sure your schema actually defines a type and not a `Connection lt T gt ` The library just needs to know how to unwrap a `Connection` and you can do that with the schema hooks You just need to implement the `willResolveMonad` hooks similar to how you unwrap a custom async class

Shane Myrick · Answer

You could use that graphql java `connectionType` to return from the `willGenerateGraphQLType` hook ```fun willGenerateGraphQLType type KType GraphQLType if type isMyConnectionType return relay connectionType else null ```

Shane Myrick · Answer

The `willResolveMonad` converts a `KType` to a `KType` that will then be used by `willGenerateGraphQLType` The end result is that you still want to have some standard GraphQL type that matches the relay spec

Filip Lastic · Answer

Okay now I understand more From what you said maybe it would better to create ` Connection` entity for each object and then I won t have to modify hook Because `relay connectionType ` needs another `GraphQLObjectType` and `GraphQLFieldDefinition` fields I am not sure if it is good idea to generate all these types in my hook