Apollo Server

typeDefs - GraphQL Schema
resolvers (an object) - defines how GraphQL queries are responded to
- all resolver functions are given four parameters¹

const { ApolloServer, gql } = require('apollo-server')
const typeDefs = gql`
  type Person {
    name: String!
    phone: String
    street: String!
    city: String! 
    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)
  }
}
const server = new ApolloServer({
  typeDefs,
  resolvers,
})
server.listen().then(({ url }) => {
  console.log(`Server ready at ${url}`)
})

Resolvers

GraphQL-server must define resolvers for each field of type in the schema
when we don't define resolvers, Apollo defined default resolvers for them
possible to define resolvers for only some fields of a type, and let the default resolvers handle the rest.

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

Resolver function signature ↩