index.js

const { ApolloServer, gql } = require('apollo-server')

let persons = [
  {
    name: "Arto Hellas",
    phone: "040-123543",
    street: "Tapiolankatu 5 A",
    city: "Espoo",
    id: "3d594650-3436-11e9-bc57-8b80ba54c431"
  },
  {
    name: "Matti Luukkainen",
    phone: "040-432342",
    street: "Malminkaari 10 A",
    city: "Helsinki",
    id: '3d599470-3436-11e9-bc57-8b80ba54c431'
  },
  {
    name: "Venla Ruuska",
    street: "Nallemäentie 22 C",
    city: "Helsinki",
    id: '3d599471-3436-11e9-bc57-8b80ba54c431'
  },
]

const typeDefs = gql`
  type Address {
    street: String!
    city: String! 
  }

  type Person {
    name: String!
    phone: String
    address: Address!
    id: ID!
  }

  type Query {
    personCount: Int!
    allPersons: [Person!]!
    findPerson(name: String!): Person
  }
`

const resolvers = {
  Query: {
    personCount: () => persons.length,
    allPersons: () => persons,
    findPerson: (root, args) =>
      persons.find(p => p.name === args.name)
  },
  Person: {
    address: (root) => {
      return {
        street: root.street,
        city: root.city
      }
    }
  }
}

const server = new ApolloServer({
  typeDefs,
  resolvers,
})

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