Introduction to Subscriptions in GraphQL

What are Subscriptions?

Subscriptions in GraphQL allow clients to listen to real-time updates from the server. When a specific event occurs, such as data creation or updates, the server sends updates to subscribed clients.

How Subscriptions Work

Subscriptions use WebSockets to maintain a persistent connection between the client and the server. Here’s a simple flow of how they work:

            graph TD;
                A[Client sends subscription request] --> B[Server accepts connection];
                B --> C[Client is subscribed to the event];
                C --> D[Event occurs on the server];
                D --> E[Server sends update to subscribed clients];
            

Implementing Subscriptions

To implement subscriptions in a GraphQL server, follow these steps:

1. Set up a WebSocket server.
2. Integrate it with your GraphQL server.
3. Define subscription types in your GraphQL schema.
4. Implement resolver functions for your subscriptions.

Here is a simple example using Apollo Server:

            const { ApolloServer, gql } = require('apollo-server');
            const { PubSub } = require('graphql-subscriptions');
            const pubsub = new PubSub();

            const typeDefs = gql`
                type Message {
                    id: ID!
                    content: String!
                }
                type Query {
                    messages: [Message]
                }
                type Subscription {
                    messageAdded: Message
                }
            `;

            const resolvers = {
                Query: {
                    messages: () => messages,
                },
                Subscription: {
                    messageAdded: {
                        subscribe: () => pubsub.asyncIterator(['MESSAGE_ADDED']),
                    },
                },
            };

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

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

Best Practices

• Keep the number of subscriptions low to prevent server overload.
• Implement authentication and authorization for sensitive data.
• Handle disconnections gracefully to maintain a good user experience.

FAQ