Building Your First GraphQL API

Tutorial · Backend Development

REST gives you fixed endpoints that return fixed shapes of data. GraphQL flips that: the client describes exactly what it wants in a single query, and the server returns exactly that shape — nothing more, nothing less.

Defining a schema

Everything in GraphQL starts with a schema — a contract describing the types your API can return and the queries clients can run.

type Book {
  id: ID!
  title: String!
  author: String!
}

type Query {
  books: [Book!]!
  book(id: ID!): Book
}

The ! marks a field as non-nullable — String! can never come back as null, which is a guarantee REST responses don't give you without extra documentation.

Writing resolvers

A resolver is the function that actually fetches the data for a field in the schema.

const books = [
  { id: '1', title: 'Dune', author: 'Frank Herbert' },
  { id: '2', title: 'Neuromancer', author: 'William Gibson' }
]

const resolvers = {
  Query: {
    books: () => books,
    book: (_, { id }) => books.find(b => b.id === id)
  }
}

Each field in the schema maps to exactly one resolver function — GraphQL calls the right one automatically based on what the client asked for.

The query the client sends

query {
  book(id: "1") {
    title
    author
  }
}

This returns only title and author — not the id, not anything else the type might have. Ask for more fields in the same query and you get them, in the same request, with no extra round-trip.

Running it

npm install apollo-server graphql

const { ApolloServer } = require('apollo-server')
const server = new ApolloServer({ typeDefs, resolvers })
server.listen().then(({ url }) => console.log(`Ready at ${url}`))

Apollo Server wires the schema and resolvers together and gives you an interactive playground to try queries immediately — a fast feedback loop while you're still learning the syntax.