Graphql Loopback Subscription PubSub

This package implements the PubSubEngine Interface from the graphql-subscriptions package and also the new AsyncIterator interface. It allows you to subscription in Loopback graphql-js.

Using as AsyncIterator

Define your GraphQL schema with a Subscription type:

schema {
  query: Query
  mutation: Mutation
  subscription: Subscription
}

type Subscription {
    somethingChanged: Result
}

type Result {
    id: String
}

Now, let's create a simple LoopbackPubSub instance:

import { LoopbackPubSub } from 'graphql-loopback-subscriptions';
const pubsub = new LoopbackPubSub();

Now, implement your Subscriptions type resolver, using the pubsub.asyncIterator to map the event you need:

const SOMETHING_CHANGED_TOPIC = 'something_changed';

export const resolvers = {
  Subscription: {
    somethingChanged: {
      subscribe: () => pubsub.asyncIterator(SOMETHING_CHANGED_TOPIC),
    },
  },
}

Subscriptions resolvers are not a function, but an object with subscribe method, that returns AsyncIterable.

Dynamically create a topic based on subscription args passed on the query:

export const resolvers = {
  Subscription: {
    somethingChanged: {
      subscribe: (_, args) => pubsub.asyncIterator(`${SOMETHING_CHANGED_TOPIC}.${args.relevantId}`),
    },
  },
}

Using both arguments and payload to filter events

import { withFilter } from 'graphql-subscriptions';

export const resolvers = {
  Subscription: {
    somethingChanged: {
      subscribe: withFilter(
        () => loopbackPubSub.asyncIterator('trigerName'),
        (payload, variables, arg0, arg1) => {
          try {
            loopbackPubSub.subscribe('trigger-name', null, variables);
          } catch (ex) {
            console.log(ex);
          }
          return true;
        },
      ),
    },
  },
}