feat: Support for Apollo Federation

[iviaks]

Closing #352

Description

Add support for Apollo Federation.

1. Added a new key directive;
2. Added support for extend type;
3. Added 3 tests for checking:
   • @key directive
   • extend type Query
   • imports

Examples

index.js

const path = require('path');
const { ApolloServer, gql } = require('apollo-server');
const { buildFederatedSchema } = require('@apollo/federation');

const { importSchema } = require('graphql-import');
const resolvers = require('./graphql/resolvers');

const typeDefs = importSchema(path.join(__dirname, './graphql/schema.graphql'));

const server = new ApolloServer({
  schema: buildFederatedSchema([
    {
      typeDefs: gql(typeDefs),
      resolvers,
    },
  ]),
});

server.listen({ port: 4001 }).then(({ url }) => {
  console.log(`🚀 Server ready at ${url}`);
});

graphql/schema.graphql

# import Query.* from './user/schema.graphql'

graphql/resolvers.js

module.exports = {
  Query: {
    me() {
      return users[0];
    },
  },
  User: {
    __resolveReference(object) {
      return users.find(user => user.id === object.id);
    },
  },
};

const users = [
  {
    id: '1',
    name: 'Ada Lovelace',
    birthDate: '1815-12-10',
    username: '@ada',
  },
  {
    id: '2',
    name: 'Alan Turing',
    birthDate: '1912-06-23',
    username: '@complete',
  },
];

graphql/user/schema.graphql

# import User from './types.graphql'

extend type Query {
  me: User
}

graphql/user/types.graphql

type User @key(fields: "id") {
  id: ID!
  name: String
  username: String
}

[drager]

@Urigo Could we get this merged?

[sponomarev]

That's a very valuable change

[sponomarev]

@iviaks Is it also necessary to add support for @requires @provides and @external directives as well as mentioned in the spec?

[iviaks]

@sponomarev, Yes. I will add a few changes as soon as possible.

[iviaks]

@sponomarev
I've added these directives and covered with tests according to Apollo Federation Docs

[shaneu]

What is the status on getting this branch merged?

[joarwilk]

@Urigo Any chance this can be merged? Would be very appreciated

[Globolobo]

@schickling Could we please get this merged?

[Alfarlost]

@Urigo, could we get this merged, please? Really a blocker for lots of people.

[marjorg]

@Urigo Any idea when this will be released?