Introduction to Apollo Server

Apollo Server is an open-source, spec-compliant GraphQL server that’s perfect for building modern web applications. It’s a community-driven project that allows developers to build a robust and fully-featured GraphQL API, and integrates seamlessly with popular JavaScript libraries and frameworks. In this post, we will delve into some of the most useful APIs provided by Apollo Server and demonstrate how to use them with comprehensive examples.

Getting Started

First, you need to install Apollo Server and its dependencies:

  npm install apollo-server graphql  

Creating a Basic Server

Here’s a simple example to get you started with Apollo Server:

  const { ApolloServer, gql } = require('apollo-server');
// Type definitions define the structure of the data const typeDefs = gql\`
  type Query {
    hello: String
  }
\`;
// Resolvers define how to fetch the types defined in the schema const resolvers = {
  Query: {
    hello: () => 'Hello World!',
  },
};
const server = new ApolloServer({ typeDefs, resolvers });
server.listen().then(({ url }) => {
  console.log(\`Server ready at ${url}\`);
});  

Integrating with Express.js

Apollo Server can be easily integrated with an existing Express.js application:

  const express = require('express'); const { ApolloServer, gql } = require('apollo-server-express');
const typeDefs = gql\`
  type Query {
    hello: String
  }
\`;
const resolvers = {
  Query: {
    hello: () => 'Hello World!',
  },
};
const server = new ApolloServer({ typeDefs, resolvers });
const app = express(); server.applyMiddleware({ app });
app.listen({ port: 4000 }, () =>
  console.log(\`Server ready at http://localhost:4000${server.graphqlPath}\`)
);  

Using Apollo Client

To make queries from a front-end application, you can use Apollo Client. Here is an example using React:

  import React from 'react'; import { ApolloProvider, ApolloClient, InMemoryCache, useQuery, gql } from '@apollo/client';
const client = new ApolloClient({
  uri: 'http://localhost:4000/graphql',
  cache: new InMemoryCache(),
});
const HELLO_QUERY = gql\`
  query GetHello {
    hello
  }
\`;
function Hello() {
  const { loading, error, data } = useQuery(HELLO_QUERY);

  if (loading) return 
Loading...
;
  if (error) return 
Error: {error.message}
;

  return 
{data.hello}
;
}
function App() {
  return (
    
      

        
My first Apollo app 🚀
        
      
    
  );
}
export default App;  

Handling Subscriptions

Apollo Server also supports WebSocket subscriptions:

  const { ApolloServer, gql, PubSub } = require('apollo-server'); const pubsub = new PubSub(); const MESSAGE_ADDED = 'MESSAGE_ADDED';
const typeDefs = gql\`
  type Message {
    id: ID!
    content: String!
  }

  type Query {
    messages: [Message!]
  }

  type Mutation {
    addMessage(content: String!): Message
  }

  type Subscription {
    messageAdded: Message
  }
\`;
const resolvers = {
  Query: {
    messages: () => [],
  },
  Mutation: {
    addMessage: (parent, { content }) => {
      const message = { id: Date.now().toString(), content };
      pubsub.publish(MESSAGE_ADDED, { messageAdded: message });
      return message;
    },
  },
  Subscription: {
    messageAdded: {
      subscribe: () => pubsub.asyncIterator([MESSAGE_ADDED]),
    },
  },
};
const server = new ApolloServer({
  typeDefs,
  resolvers,
  subscriptions: {
    path: '/subscriptions',
  },
});
server.listen().then(({ url, subscriptionsUrl }) => {
  console.log(\`Server ready at ${url}\`);
  console.log(\`Subscriptions ready at ${subscriptionsUrl}\`);
});  

Conclusion

Apollo Server is a versatile and powerful tool for building GraphQL APIs. With its easy integration with various libraries and frameworks, along with comprehensive features such as subscriptions, it is an excellent choice for modern web development. Happy coding!

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