Subscription
In GraphQL, Subscription allows the server to push data to the client.
Basic Usage
In GQLoom, we use the subscription function to define a subscription:.
import { weave, resolver, subscription } from "@gqloom/core"
import { ValibotWeaver } from "@gqloom/valibot"
import * as v from "valibot"
import { createServer } from "node:http"
import { createYoga } from "graphql-yoga"
const CountdownResolver = resolver({
countdown: subscription(v.number(), {
input: { seconds: v.pipe(v.number(), v.integer()) },
subscribe: async function* (data) {
for (let i = data.seconds; i >= 0; i--) {
await new Promise((resolve) => setTimeout(resolve, 1000))
yield i
}
},
}),
})
const schema = weave(CountdownResolver)
const yoga = createYoga({ schema })
const server = createServer(yoga)
server.listen(4000, () => {
console.info("Server is running on http://localhost:4000/graphql")
})
In the code above, we define a countdown subscription that accepts a seconds parameter.
We passed in an asynchronous generator in the subscription function, which will push a number every second until the number is 0.
Using publish/subscribe
We can also use the publish/subscribe feature provided by GraphQL Yoga to push messages more easily:
import { resolver, query, subscription } from "@gqloom/core"
import { createPubSub } from "graphql-yoga"
import * as v from "valibot"
const pubSub = createPubSub<{ greeting: [string] }>()
const HelloResolver = resolver({
hello: query(v.string(), {
input: { name: v.string() },
resolve: ({ name }) => {
const hello = `Hello, ${name}`
pubSub.publish("greeting", hello)
return hello
},
}),
listenGreeting: subscription(v.string(), {
subscribe: () => pubSub.subscribe("greeting"),
resolve: (payload) => payload,
}),
})
In the code above, we defined a hello query and a listenGreeting subscription.
When the hello query is called, it publishes a greeting event, and the listenGreeting subscription subscribes to this event and pushes a message when it occurs.
You can learn about the detailed usage of the Publish/Subscribe feature at GraphQL Yoga Documentation.
Using Subscriptions in Distributed Systems
The subscription feature can work easily in a monolithic application. However, in a distributed system, the subscription feature can get complicated. You may consider using the event-driven federated subscription feature from WunderGraph Cosmo to handle subscriptions in a distributed system.
