Implementing and testing GraphQL subscriptions

Subscription is another GraphQL root type that sends the object to the subscriber (client) when a particular event occurs.

Let’s assume an online shop offers a discount on products when the product’s inventory reaches a certain level. You cannot track each product’s quantity manually and then perform the computation and trigger the discount. To do things faster (or reduce manual intervention), this is where you can make use of a subscription.

Each change in the product’s inventory (quantity) through the addQuantity() mutation should trigger the event and the subscriber should receive the updated product and hence the quantity. Then, the subscriber can place the logic and automate this process.

Let’s write the subscription that will send the updated product object to the subscriber. You are going to use Reactive Streams and WebSocket to implement this functionality.

You need to enable CORS...