reviews.js

const { ApolloServer } = require('apollo-server')
const { buildFederatedSchema } = require('@apollo/federation')
const { post } = require('httpie')
const { parse } = require('graphql')

const typeDefs = /* GraphQL */ `
  type Review @key(fields: "id") {
    id: ID!
    body: String
    author: User @provides(fields: "username")
    product: Product
  }

  extend type User @key(fields: "id") {
    id: ID! @external
    username: String @external
    reviews: [Review]
  }

  extend type Product @key(fields: "upc") {
    upc: String! @external
    reviews: [Review]
  }
`

async function main() {
  // Push schema to registry
  await post(`http://localhost:3000/schema/push`, {
    body: {
      typeDefs: typeDefs,
      graphName: 'my_graph',
      serviceName: 'reviews',
      routingUrl: 'http://localhost:4002/graphql',
    },
  })
  startServer()
}

function startServer() {
  const resolvers = {
    Review: {
      author(review) {
        return { __typename: 'User', id: review.authorID }
      },
    },
    User: {
      reviews(user) {
        return reviews.filter((review) => review.authorID === user.id)
      },
      numberOfReviews(user) {
        return reviews.filter((review) => review.authorID === user.id).length
      },
      username(user) {
        const found = usernames.find((username) => username.id === user.id)
        return found ? found.username : null
      },
    },
    Product: {
      reviews(product) {
        return reviews.filter((review) => review.product.upc === product.upc)
      },
    },
  }

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

  server.listen({ port: 4002 }).then(({ url }) => {
    console.log(`🚀 Server ready at ${url}`)
  })

  const usernames = [
    { id: '1', username: '@ada' },
    { id: '2', username: '@complete' },
  ]
  const reviews = [
    {
      id: '1',
      authorID: '1',
      product: { upc: '1' },
      body: 'Love it!',
    },
    {
      id: '2',
      authorID: '1',
      product: { upc: '2' },
      body: 'Too expensive.',
    },
    {
      id: '3',
      authorID: '2',
      product: { upc: '3' },
      body: 'Could be better.',
    },
    {
      id: '4',
      authorID: '2',
      product: { upc: '1' },
      body: 'Prefer something else.',
    },
  ]
}

main().catch((err) => {
  console.error(err)
  process.exit(1)
})