Graphql no resolver definied for interface/union - java

Question

I have problem adding resolver using this approach in graphql:

@RestController
@RequestMapping("/api/dictionary/")
@RequiredArgsConstructor(onConstructor = @__(@Autowired))
public class DictionaryController {
    @Value("classpath:items.graphqls")
    private Resource schemaResource;
    private GraphQL graphQL;
    private final DictionaryService dictionaryService;

    @PostConstruct
    public void loadSchema() throws IOException {
        File schemaFile = schemaResource.getFile();
        TypeDefinitionRegistry registry = new SchemaParser().parse(schemaFile);
        RuntimeWiring wiring = buildWiring();
        GraphQLSchema schema = new SchemaGenerator().makeExecutableSchema(registry, wiring);
        graphQL = GraphQL.newGraphQL(schema).build();
    }

private RuntimeWiring buildWiring() {
    DataFetcher<List<DictionaryItemWithParentDto>> fetcher6 = dataFetchingEnvironment -> dictionaryService.getClaimSubType();

        return RuntimeWiring.newRuntimeWiring()
                .type("Query", typeWriting ->
                   typeWriting
                    .dataFetcher("getClaimSubType", fetcher6)
                    )
                .build();
    }


public List<DictionaryItemWithParentDto> getClaimSubType() {
    return dictionaryService.getClaimSubType();
   }
  }

items.graphqls file content:

type Query {
    getClaimSubType: [DictionaryItemWithParentDto]
}

type DictionaryItemWithParentDto {
    code: String!
    name: String
    parents: [DictionaryItemDto]
}

type DictionaryItemDto {
    code: String!
    name: String
    description: String
}

In java I have Vehicle interface and two classes that implement it: Airplane and Car. When i add to schema this line:

union SearchResult = Airplane | Car

I get following error:

There is no type resolver defined for interface / union 'Vehicle' type, There is no type resolver defined for interface / union 'SearchResult' type]}

I am not sure how to handle it.

If instead i add:

interface Vehicle {
    maxSpeed: Int
}

type Airplane implements Vehicle {
    maxSpeed: Int
    wingspan: Int
}

type Car implements Vehicle {
    maxSpeed: Int
    licensePlate: String
}

I get following error:

errors=[There is no type resolver defined for interface / union 'Vehicle' type]

How can i handle these errors using my approach ? Is there another approach to handle it?

Edit

Adding these lines of code fix the issue partway i guess:

TypeResolver t =  new TypeResolver() {
    @Override
    public GraphQLObjectType getType(TypeResolutionEnvironment env) {
        Object javaObject = env.getObject();
        if (javaObject instanceof Car) {
            return env.getSchema().getObjectType("Car");
        } else if (javaObject instanceof Airplane) {
            return env.getSchema().getObjectType("Airplane");
        } else {
            return env.getSchema().getObjectType("Car");
        }
    }
};

And adding to RuntimeWiring builder this:

            .type("Vehicle", typeWriting ->
                    typeWriting
                            .typeResolver(t)
            )


    @PostMapping("getVehicle")
    public ResponseEntity<Object> getVehicleMaxSpeed(@RequestBody String query) 
   {
        ExecutionResult result = graphQL.execute(query);
        return new ResponseEntity<Object>(result, HttpStatus.OK);
    }

When asking for:

query {
    getVehicle(maxSpeed: 30) {
        maxSpeed

    }
}

I get the maxSpeed but when i add wingspan i get an error

Field 'wingspan' in type 'Vehicle' is undefined @ 'getVehicle/wingspan'",

I added

getVehicle(maxSpeed: Int): Vehicle

To the graphqls file. I thought that polymorphism would work here.

Lamoureux

Answer 1

Adding these lines of code fix the issue:

TypeResolver t =  new TypeResolver() {
    @Override
    public GraphQLObjectType getType(TypeResolutionEnvironment env) {
        Object javaObject = env.getObject();
        if (javaObject instanceof Car) {
            return env.getSchema().getObjectType("Car");
        } else if (javaObject instanceof Airplane) {
            return env.getSchema().getObjectType("Airplane");
        } else {
            return env.getSchema().getObjectType("Car");
        }
    }
};

And adding to RuntimeWiring builder this:

            .type("Vehicle", typeWriting ->
                    typeWriting
                            .typeResolver(t)
            )


    @PostMapping("getVehicle")
    public ResponseEntity<Object> getVehicleMaxSpeed(@RequestBody String query) 
   {
        ExecutionResult result = graphQL.execute(query);
        return new ResponseEntity<Object>(result, HttpStatus.OK);
    }

When asking for:

query {
    getVehicle(maxSpeed: 30) {
        maxSpeed

    }
}

I get the maxSpeed but when i add wingspan i get an error

Field 'wingspan' in type 'Vehicle' is undefined @ 'getVehicle/wingspan'",

I added

getVehicle(maxSpeed: Int): Vehicle

To the graphqls file. I thought that polymorphism would work here.

If i want fields from subclasses i can ask for them like that:

query {
    getVehicle(maxSpeed: 10) {
        maxSpeed
        ... on Airplane {
        wingspan
      }
        ... on Car {
        licensePlate
      }
    }
}

Lamoureux

how did you compile this line? if (javaObject instanceof Car) { how this CAR class is generated? – Extemporize

It's normal Java class - made by hand – Lamoureux

Is there a generic way to do it without creating the Car class? – Vanguard

@Vanguard I have checked if javaObject instanceof Map && ((Map)javaObject).get("__typename") and put the type name directly into the map value. You can do anything you want to determine the GraphQL type name, given a value, it doesn't have to be concrete-class-based (though it is a very Java-idiomatic option) – Interaction