Subscriptions

You can add a subscription to your schema by defining a subscription type and then attaching resolvers to it. All subscription resolvers must return an AsyncIterator.t with a valid GraphQL type.

Let's look at an example:

// Define the subscription type
@gql.type
type subscription

let wait = ms => {
  Promise.make((resolve, _) => {
    let _ = setTimeout(() => resolve(), ms)
  })
}

@gql.field
let countdown = (_: subscription, ~from: int) => {
  let countdown = ref(from)
  let iterator = AsyncIterator.make(async () => {
    await wait(500)
    let current = countdown.contents
    countdown := current - 1

    if current > 0 {
      AsyncIterator.value(current)
    } else {
      AsyncIterator.done(~finalValue=current)
    }
  })

  iterator
}

This would produce the following schema:

type Subscription {
  countdown(from: Int!): Int!
}