Building GraphQL APIs: Modern API Development

What is GraphQL?

GraphQL is a query language for APIs that allows clients to request exactly the data they need. Unlike REST, GraphQL uses a single endpoint and lets clients specify their data requirements.

Setting Up GraphQL Server

npm install apollo-server express graphql

// server.js
const { ApolloServer, gql } = require('apollo-server-express');
const express = require('express');

const typeDefs = gql`
  type User {
    id: ID!
    name: String!
    email: String!
    posts: [Post!]!
  }

  type Post {
    id: ID!
    title: String!
    content: String!
    author: User!
  }

  type Query {
    users: [User!]!
    user(id: ID!): User
    posts: [Post!]!
  }

  type Mutation {
    createUser(name: String!, email: String!): User!
    createPost(title: String!, content: String!, authorId: ID!): Post!
  }
`;

const resolvers = {
  Query: {
    users: () => users,
    user: (parent, args) => users.find(u => u.id === args.id),
    posts: () => posts
  },
  Mutation: {
    createUser: (parent, args) => {
      const user = { id: String(users.length + 1), ...args, posts: [] };
      users.push(user);
      return user;
    },
    createPost: (parent, args) => {
      const post = { id: String(posts.length + 1), ...args };
      posts.push(post);
      return post;
    }
  },
  User: {
    posts: (parent) => posts.filter(p => p.authorId === parent.id)
  }
};

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

server.applyMiddleware({ app });

app.listen(4000, () => {
  console.log(`Server ready at http://localhost:4000${server.graphqlPath}`);
});

Querying GraphQL

# Query example
query {
  users {
    id
    name
    email
    posts {
      title
      content
    }
  }
}

# Mutation example
mutation {
  createUser(name: "John", email: "john@example.com") {
    id
    name
  }
}

Advantages of GraphQL

• Efficient: Fetch only needed data
• Type-safe: Strong typing system
• Single endpoint: One endpoint for all operations
• Real-time: Built-in subscriptions support