Get Started

# ===== Server (Apollo Server, Node) =====
mkdir gql-demo && cd gql-demo
npm init -y
npm install @apollo/server graphql

# server.mjs
import { ApolloServer } from '@apollo/server';
import { startStandaloneServer } from '@apollo/server/standalone';

const typeDefs = \`
  type Book {
    id: ID!
    title: String!
    author: String!
  }
  type Query {
    books: [Book!]!
    book(id: ID!): Book
  }
  type Mutation {
    addBook(title: String!, author: String!): Book!
  }
\`;

const data = [
  { id: '1', title: 'The Pragmatic Programmer', author: 'Hunt & Thomas' },
];

const resolvers = {
  Query: {
    books: () => data,
    book: (_, { id }) => data.find(b => b.id === id),
  },
  Mutation: {
    addBook: (_, { title, author }) => {
      const b = { id: String(data.length + 1), title, author };
      data.push(b);
      return b;
    },
  },
};

const server = new ApolloServer({ typeDefs, resolvers });
const { url } = await startStandaloneServer(server, { listen: { port: 4000 } });
console.log('Ready at', url);

# Run:
node server.mjs
# Visit http://localhost:4000 — Apollo Studio sandbox loads.

# ===== A query =====
# In the sandbox:
query {
  books { id title author }
  book(id: "1") { title }
}

# A mutation:
mutation {
  addBook(title: "Refactoring", author: "Fowler") { id title }
}

# ===== Client (urql) =====
npm install @urql/core graphql

// client.mjs
import { Client, cacheExchange, fetchExchange } from '@urql/core';
const client = new Client({ url: 'http://localhost:4000', exchanges: [cacheExchange, fetchExchange] });

const r = await client.query('{ books { id title } }', {}).toPromise();
console.log(r.data.books);

# ===== With variables =====
const VARS = \`query Get($id: ID!) { book(id: $id) { title author } }\`;
const r2 = await client.query(VARS, { id: '1' }).toPromise();

# ===== Where to go next =====
# - Schema-first design (organise typeDefs in .graphql files)
# - DataLoader for batching DB lookups (N+1)
# - Code generation (graphql-codegen) for typed clients
# - Authn / authz in context
# - Persisted queries on public APIs

# ===== Patterns to internalise =====
# - Start with a tiny schema; iterate
# - Resolver gets (parent, args, context, info) — use args for arguments
# - Apollo Studio for instant docs / playground
# - Use context for auth + datasource handles

# ===== Pitfalls =====
# - One mega-Query type with everything attached
# - Returning bare Promise<Mongoose> -> serialises private fields
# - No query depth limit on a public API
# - Throwing strings instead of GraphQLError (loses error shape)

npm init -y
npm install graphql graphql-yoga
# Then write a schema + resolvers; ship.