In this blog post, we will explore how to use GraphQL subscriptions with Express.js and Apollo Server to achieve real-time data updates in your web application. Real-time updates are vital for applications that require immediate data changes, such as chat applications, real-time monitoring, or collaborative editing platforms.

What are GraphQL Subscriptions?

GraphQL subscriptions allow clients to subscribe to certain data events and receive real-time updates from the server when those events occur. Unlike traditional GraphQL queries and mutations that are request-response based, subscriptions establish a long-lived connection between the client and the server to enable real-time communication.

Prerequisites

To follow along with this tutorial, you’ll need:

• Basic knowledge of GraphQL and its concepts
• Node.js and npm installed on your machine
• Express.js and Apollo Server set up in your project

Setting up GraphQL Subscriptions

To start using GraphQL subscriptions, we first need to set up the required dependencies and configure our server.

Installation

Open your terminal and navigate to your project directory. Install the necessary dependencies:

$ npm install graphql-subscriptions graphql-yoga

Implementing Subscriptions in Apollo Server

Next, we need to configure our Apollo Server to use GraphQL subscriptions. Here’s an example of how you can set up subscriptions with Apollo Server and Express.js:

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

const app = express();
const pubsub = new PubSub();

const typeDefs = `
  type Subscription {
    newPost: Post!
  }

  type Post {
    id: ID!
    title: String!
  }

  type Query {
    posts: [Post!]!
  }
`;

const posts = [];

const resolvers = {
  Subscription: {
    newPost: {
      subscribe: () => pubsub.asyncIterator(['NEW_POST']),
    },
  },
  Query: {
    posts: () => posts,
  },
};

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

server.applyMiddleware({ app });

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

In this example, we first import the necessary dependencies. We create an instance of the PubSub class from the apollo-server-express package, which will handle the publication and subscription logic.

We define our GraphQL schema with a new Subscription type that includes the newPost event. We also define a Query type with a posts field to fetch existing posts.

We initialize an empty posts array as a temporary data store for demonstration purposes in this example.

We implement the newPost subscription resolver, where we subscribe to the NEW_POST event using the pubsub.asyncIterator function.

Finally, we create an instance of the Apollo Server and apply it to our Express.js app. The server listens for incoming connections on port 4000.

Testing Subscriptions

To test our subscriptions, we can use a GraphQL client or the built-in Playground tool provided by Apollo Server.

1. Open your browser and navigate to http://localhost:4000/graphql.
2. In the Playground application, run the following subscription query in a separate tab:

subscription {
  newPost {
    id
    title
  }
}

1. In another tab, execute a mutation to create a new post:

mutation {
  createPost(title: "New Post") {
    id
    title
  }
}

You should see the new post being emitted through the subscription and received by the client in real-time.

Conclusion

In this blog post, we explored how to use GraphQL subscriptions with Express.js and Apollo Server to implement real-time data updates in a web application. Subscriptions are a powerful tool for building interactive and dynamic experiences where immediate data changes are crucial.

By following the steps outlined in this tutorial, you should now have a good understanding of how to set up GraphQL subscriptions and implement them in your Express.js and Apollo Server-based applications.

#GraphQL #Subscriptions