graphql-ably-pubsub

graphql-ably-pubsub

Ably is a pub/sub messaging platform with a suite of integrated services to deliver complete realtime functionality directly to end-users. In the context of GraphQL, we can use it to publish when a mutation is fired and subscribe to the result through a subscription query.

This package implements the PubSubEngine Interface from the graphql-subscriptions package and also the new AsyncIterator interface. It allows you to connect your subscription manger to an Ably PubSub mechanism to support multiple subscription manager instances.

Installation

npm install graphql-ably-pubsub or yarn add graphql-ably-pubsub

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 AblyPubSub instance:

import { AblyPubSub } from "graphql-ably-pubsub";
const pubsub = new AblyPubSub();

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.

Calling the method asyncIterator of the AblyPubSub instance will subscribe to the topic provided and will return an AsyncIterator bound to the AblyPubSub instance and listens to any event published on that topic. Now, the GraphQL engine knows that somethingChanged is a subscription, and every time we will use pubsub.publish over this topic, the AblyPubSub will PUBLISH the event to all other subscribed instances and those in their turn will emit the event to GraphQL using the next callback given by the GraphQL engine.

pubsub.publish(SOMETHING_CHANGED_TOPIC, { somethingChanged: { id: "123" } });

Dynamically use 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(
        (_, args) =>
          pubsub.asyncIterator(`${SOMETHING_CHANGED_TOPIC}.${args.relevantId}`),
        (payload, variables) =>
          payload.somethingChanged.id === variables.relevantId
      ),
    },
  },
};

Creating the Ably Client

import { AblyPubSub } from "graphql-ably-pubsub";

const pubSub = new AblyPubSub(options, channelName, pubSubClient);

Options

These are the options which are passed to the internal or passed Ably PubSub client. Example -

const options = {
  key: "<YOUR-ABLY-API-KEY>",
};

channelName (optional)

If specified, this channel name is used for every trigger otherwise the trigger itself is used as the channel name. Example -

const channel = "ably-subscription-channel";

pubSubClient (optional)

If specified, then this client will be used and the options param value will be ignored. Example -

const options = {
  key: "<YOUR-ABLY-API-KEY>",
};
const pubSubClient = new Ably.Realtime(options);

Acknowledgements

This project is mostly inspired by graphql-redis-subscriptions and graphql-google-pubsub. Thanks to its authors for their work and inspiration.