GraphQL Subscriptions Setup

1. Introduction

GraphQL Subscriptions allow clients to subscribe to real-time updates from the server. Unlike queries and mutations that are one-time requests, subscriptions enable a persistent connection for ongoing data retrieval. This lesson covers the fundamentals of setting up GraphQL subscriptions in your application.

2. Key Concepts

• Subscription: A request for real-time updates.
• WebSocket: A protocol used to establish a persistent connection for real-time communication.
• Pub/Sub: A messaging pattern where subscribers receive messages published by a publisher.

3. Setup

3.1 Install Required Packages

To implement GraphQL subscriptions, you need to install the following packages:

npm install graphql subscriptions-transport-ws

3.2 Server Configuration

Integrate WebSocket support into your GraphQL server:

const { ApolloServer } = require('apollo-server');
const { SubscriptionServer } = require('subscriptions-transport-ws');
const { execute, subscribe } = require('graphql');
const WebSocket = require('ws');

const server = new ApolloServer({ /* your config */ });

const ws = new WebSocket.Server({ server: httpServer });

ws.on('connection', (connection) => {
    new SubscriptionServer({
        execute,
        subscribe,
        schema: yourGraphQLSchema,
    }, {
        server: connection,
        path: '/subscriptions',
    });
});
        

4. Code Example

4.1 Defining a Subscription

Define your subscription in the GraphQL schema:

const typeDefs = gql`
    type Message {
        id: ID!
        content: String!
    }

    type Subscription {
        messageSent: Message
    }
`;
        

4.2 Publishing Updates

Publish updates to subscribers when an event occurs:

const { PubSub } = require('graphql-subscriptions');
const pubsub = new PubSub();

const resolvers = {
    Subscription: {
        messageSent: {
            subscribe: () => pubsub.asyncIterator('MESSAGE_SENT')
        }
    },
    Mutation: {
        sendMessage: (parent, { content }) => {
            const message = { id: '1', content };
            pubsub.publish('MESSAGE_SENT', { messageSent: message });
            return message;
        }
    }
};
        

5. Best Practices

• Use efficient filtering mechanisms to limit the data sent to clients.
• Implement error handling and reconnection strategies for WebSocket.
• Test subscription performance under various load conditions.

6. FAQ