Java GraphQL Spring Boot Apollo federation issue with reference resolver

Question

I am trying to get Apollo federation working with two GraphQL services using Java/Spring Boot and graphql-kickstart. Consider the following schemas:

Person Service:

type Person @key(fields: "id") {
  id: String!
  name: String!
}

Book Service:

type Book @key(fields: "id") {
  id: String!
  author: Person!
}

type Person @extends @key(fields: "id") {
  id: String! @external
}

I am trying to run a query such as:

query {
  book(bookId:"1") {
    author {
      name
    }
  }
}

When I run the query against the Apollo gateway, the query it runs against the Person service is:

query ($representations:[_Any!]!) {
  _entities(representations:$representations) {
    ... on Person {
      name
    }
  }
}

with variables:

{
  "representations": [
    {
      "__typename": "Person",
      "id": "2"
    }
  ]
}

This is returning:

{
  "data": {
    "_entities": [null]
  }
}

GraphQL configuration (class with @Configuration annotation) has the following (taken from the example at https://github.com/setchy/graphql-java-kickstart-federation-example/blob/master/shows/src/main/java/com/example/demo/federation/FederatedSchema.java):

    @Bean
    public GraphQLSchema customSchema(SchemaParser schemaParser) {
        GraphQLSchema federatedSchema = Federation.transform(schemaParser.makeExecutableSchema())
            .fetchEntities(env -> env.<List<Map<String, Object>>>getArgument(_Entity.argumentName)
                .stream()
                .map(reference -> {
                    return null;
                })
                .collect(Collectors.toList()))
            .resolveEntityType(env -> {
                return null;
            })
            .build();

        return federatedSchema;
    }

According to the Apollo documentation at https://www.apollographql.com/docs/federation/entities/#2-define-a-reference-resolver the .fetchEntities method should add a reference resolver that resolves the type. However, I'm unsure how to do this in a static context, and in the example linked above this is not done (although I'm unable to get the example to work due to a separate issue).

Any ideas to help point out what's wrong are appreciated.

Procrastinator · Accepted Answer · 2023-05-03 06:34:30Z

0

Since you are not contributing any fields to the Person, I think you need to define it like this

Book Service:

type Book @key(fields: "id") {
  id: String!
  author: Person!
}

type Person @extends @key(fields: "id", resolvable: false) {
  id: String!
}

edited May 3, 2023 at 6:34

Procrastinator

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answered Apr 28, 2023 at 19:02

DIY Maverick

1

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