Unlock the Power of Real-Time Data with GraphQL Subscriptions
Have you ever wondered how social media platforms and mapping services update your feed and location in real-time? The answer lies in GraphQL subscriptions, a game-changing technology that enables seamless communication between clients and servers.
What are GraphQL Subscriptions?
GraphQL subscriptions allow you to subscribe to events under a source stream and receive notifications in real-time via the response stream when the selected event executes. This innovative approach enables efficient handling of event-driven systems at scale.
How Do GraphQL Subscriptions Work?
When a GraphQL subscription is executed, a persistent function is created on the server that maps an underlying source stream to a returned response stream. This facilitates a publisher/subscriber mechanism, where data flows according to the queue principle (first in, first out) to the subscriber.
Building a GraphQL Application with Subscriptions
To demonstrate the power of GraphQL subscriptions, we’ll build a Node.js server that performs CRUD operations on a JSON file. We’ll use the graphql-yoga module, which provides all necessary dependencies and server bindings with Node.js under the hood.
Getting Started
First, create a new folder and initialize it with a package.json file. Then, install the required dependencies and create the necessary files: index.js, postData.json, typeDefs.js, and resolvers.js.
Defining Our Schema
In typeDefs.js, we’ll create schemas for our operations, including a custom Subscription type that triggers events when changes are made to a post object.
Coding Our Resolvers
In resolvers.js, we’ll define our Query, Mutation, and Subscription objects. We’ll flesh out each object in the sections below.
Query Object
We’ll define two queries, getPosts and getPost, to read all posts and a specific post by ID, respectively.
Mutation Object
We’ll define three mutations: createPost, updatePost, and deletePost. Each mutation will publish an event to all subscribers of the post channel through the socket with the relevant post data in its payload.
Subscription Object
We’ll add our subscription object, which uses a pubsub.asyncIterator function to map the event underlying the source stream to a returned response stream.
Running Our Project
Finally, we’ll add a script to run our project in package.json and start the server. Open the terminal and run npm start. If everything is working well, you’ll see a GraphQL Playground instance.
Testing Our Subscription
To confirm that everything is working correctly, run a getPosts query and then perform any of the mutations in a new tab. Notice how the post response stream returns the data for the update event.
Recapping the GraphQL Subscription Process
To recap, the subscription process involves defining the subscription type resolver, using the pub/sub method provided by graphql-yoga to subscribe and publish, and implementing the subscription type resolver to map the event using pubsub.asyncIterator.
Conclusion
By implementing GraphQL subscriptions, you can create real-time notifications whenever a selected event is executed. With this powerful technology, you can take your application to the next level and provide a seamless user experience.