getResolversFromSchema fails to extract Federation __resolveReference resolvers

[darrellwarde]

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---

Describe the bug

getResolversFromSchema seems to fail to extract __resolveReference resolvers from a subgraph schema.

To Reproduce
Steps to reproduce the behavior:

Run the following code:

const { buildSubgraphSchema } = require("@apollo/subgraph");
const { getResolversFromSchema } = require("@graphql-tools/utils");
const { gql } = require("graphql-tag");

const typeDefs = gql`
  type User @key(fields: "id") {
    id: ID!
  }

  type Query {
    user: User!
  }
`;

const resolvers = {
  User: {
    __resolveReference: () => ({ id: 1 })
  },
  Query: {
    user: () => ({ id: 1 })
  }
};

const schema = buildSubgraphSchema({
  typeDefs,
  resolvers
});

const extractedResolvers = getResolversFromSchema(schema);

console.log(extractedResolvers);

The output is as follows:

[Object: null prototype] {
  User: {},
  Query: {
    user: { resolve: [Function: user] },
    _entities: { resolve: [Function: _entities] },
    _service: { resolve: [Function: _service] }
  },
  _FieldSet: GraphQLScalarType {
    name: '_FieldSet',
    description: undefined,
    specifiedByURL: undefined,
    serialize: [Function: identityFunc],
    parseValue: [Function: identityFunc],
    parseLiteral: [Function (anonymous)],
    extensions: [Object: null prototype] {},
    astNode: undefined,
    extensionASTNodes: []
  },
  _Any: GraphQLScalarType {
    name: '_Any',
    description: undefined,
    specifiedByURL: undefined,
    serialize: [Function: identityFunc],
    parseValue: [Function: identityFunc],
    parseLiteral: [Function (anonymous)],
    extensions: [Object: null prototype] {},
    astNode: undefined,
    extensionASTNodes: []
  },
  _Service: {},
  _Entity: { __resolveType: [Function: __resolveType] }
}

You can see that the User type has lost its __resolveReference resolver.

Expected behavior

I would expect to see the __resolveReference resolvers which I defined within the output.

Environment:

• OS: macOS 12.5.1
• @graphql-tools/utils: 8.12.0
• NodeJS: 16.13.0

[ardatan]

This is not a bug in GraphQL Tools actually but a feature request for getResoiversFromSchema to support Apollo's specific extensions in the resolvers map.
Also see #2687 (comment)

[darrellwarde]

Interesting, thanks for the prompt response!

It sounds a bit like lunacy, but I'm looking at executing buildSubgraphSchema, extracting the relevant parts, performing some other actions on them, and finally passing all of that into makeExecutableSchema - do you know if there's a combination of existing functions that can be used to extract everything I need, so that the output of makeExecutableSchema is the same as the output as buildSubgraphSchema? It seems that the __resolveReference resolvers are passed into the extensions of the GraphQL schema - is it possible for extensions to be extracted and passed into makeExecutableSchema right now?

[ardatan]

It seems Apollo is putting resolveReference under extensions. Maybe you can use that;
https://github.com/apollographql/federation/blob/main/subgraph-js/src/schema-helper/buildSchemaFromSDL.ts#L181