Introduction to Apollo Server

Apollo Server is a popular, open-source GraphQL server that enables you to quickly build a production-ready, self-documenting API. In this guide, we will introduce Apollo Server and explore its various functionalities with code snippets.

Setting Up Apollo Server

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

// Type Definitions
const typeDefs = gql`
  type Query {
    hello: String
  }
`;

// Resolvers
const resolvers = {
  Query: {
    hello: () => 'Hello, world!',
  },
};

// Apollo Server Instantiation
const server = new ApolloServer({ typeDefs, resolvers });

// Listening on a port
server.listen().then(({ url }) => {
  console.log(`Server ready at ${url}`);
});

Multiple Queries and Mutations

You can define multiple query and mutation types in your schema:

const typeDefs = gql`
  type Book {
    title: String
    author: String
  }

  type Query {
    books: [Book]
  }

  type Mutation {
    addBook(title: String, author: String): Book
  }
`;

const books = [];

const resolvers = {
  Query: {
    books: () => books,
  },
  Mutation: {
    addBook: (parent, args) => {
      const newBook = { title: args.title, author: args.author };
      books.push(newBook);
      return newBook;
    },
  },
};

Integrating Apollo Server with Express

You can also integrate Apollo Server with an existing Express application:

const express = require('express');
const { ApolloServer } = require('apollo-server-express');

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

server.applyMiddleware({ app });

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

Context

Providing a context to every resolver allows you to pass user authentication details, data loaders, etc.:

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: ({ req }) => {
    // For example, user authentication
    const token = req.headers.authorization || '';
    // Extract the user from the token
    // This is just an example; implement your own auth logic here.
    const user = getUserFromToken(token);
    return { user };
  },
});

Error Handling

Handle errors gracefully in your resolvers:

const resolvers = {
  Query: {
    books: () => {
      try {
        // Your logic here
        return books;
      } catch (error) {
        throw new Error('Something went wrong');
      }
    },
  },
};

A Complete Example

Here is a complete example application using Apollo Server:

const { ApolloServer, gql } = require('apollo-server');
const books = [
  { title: 'Harry Potter and the Chamber of Secrets', author: 'J.K. Rowling' },
  { title: 'Jurassic Park', author: 'Michael Crichton' },
];

const typeDefs = gql`
  type Book {
    title: String
    author: String
  }

  type Query {
    books: [Book]
  }

  type Mutation {
    addBook(title: String, author: String): Book
  }
`;

const resolvers = {
  Query: {
    books: () => books,
  },
  Mutation: {
    addBook: (parent, args) => {
      const newBook = { title: args.title, author: args.author };
      books.push(newBook);
      return newBook;
    },
  },
};

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

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

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