graphql-firestore-subscriptions

graphql-firestore-subscriptions implements the PubSubEngine interface from the graphql-subscriptions package.

Unlike other databases, Goole's Firestore comes across with real time updates. Therefore, it is not required to publish events to a queue or a pub-sub. However, there is still something to do to get the data to the clients. In graphql-firestore-subscriptions thus tasks are called handlers. They are subscribing a specific topic and broadcast whatever you want over an AsyncIterator which is compatible with graphql-subscriptions.

Usage

First of all, you have to install the graphql-firestore-subscriptions package using yarn or npm by calling either yarn add graphql-firestore-subscriptions or npm i --save graphql-firestore-subscriptions.

Create a new graphql-firestore-subscription instance

import PubSub from 'graphql-firestore-subscriptions';
 
const ps = new PubSub();

Adding handlers

A handler gets two arguments:

• The broadcast function itself to send new data
• An object with options

Note, that the handler MUST return a unsubscribe function.

ps.registerHandler(() => {
  // subscribe to a topic
  return () => {
    // unsubscribe
  };
});

The unsubscribe function can either return void or a boolean value. If a boolean value is returned by the unsubscribe function, the PubSubEngine will throw an error if the return value is falsey.

Advanced handlers

Unlike other graphql-subscriptions, graphql-firestore-subscriptions requires a handler for each topic you are about to subscribe. To make the handler-creation as easy as possibile graphql-firestore-subscriptions comes across with a bunch of utility functions.

The following example shows a simple fall-through handler which takes document changes of a collection to broadcast this changes immediately.

import PubSub, { createFallThroughHandler } from 'graphql-firestore-subscriptions';
import db from '../path/to/firestore/conenction';
 
// ...
 
enum Topic {
  NEW_COMMENT = 'NEW_COMMENT',
}
 
ps.registerHandler(
  ...createFallThroughHandler(db, {
    topic: Topic.NEW_COMMENT,
    collection: 'comment',
    filter: ['added'],
  })
);

You can also create multiple fall-through handlers at once:

import PubSub, { createFallThroughHandlerFromMap } from 'graphql-firestore-subscriptions';
import db from '../path/to/firestore/conenction';
 
// ...
 
enum Topic {
  NEW_COMMENT = 'NEW_COMMENT',
  UPDATE_COMMENT = 'UPDATE_COMMENT',
}
 
createFallThroughHandlerFromMap(db, {
  [Topic.NEW_COMMENT]: {
    collection: 'comment',
    filter: ['added'],
  },
  [Topic.UPDATE_COMMENT]: {
    collection: 'comment',
    filter: ['modified'],
  },
}).forEach((topic, handler) => ps.registerHandler(topic, handler));

See API for additional information about how createFallThroughHandlerFromMap / createFallThroughHandler work.

Full example

import PubSub from 'graphql-firestore-subscriptions';
import db from '../path/to/firestore/conenction';
 
enum Topic {
  NEW_COMMENT = 'NEW_COMMENT',
}
 
const ps = new PubSub();
 
ps.registerHandler(Topic.NEW_COMMENT, broadcast =>
  // Note, that `onSnapshot` returns a unsubscribe function which
  // returns void.
  db.collection('comments').onSnapshot(snapshot => {
    snapshot
      .docChanges()
      .filter(change => change.type === 'added')
      .map(item => broadcast(item.data()));
  })
);
 
const iterator = ps.asyncIterator(Topic.NEW_COMMENT);
const addedComment = await iterator.next();
 
// ...

With apollo-server-graphql

Define a GraphQL schema with a Subscription type.

schema {
  query: Query
  mutation: Mutation
  subscription: Subscription
}
 
type Subscription {
  newComment: Comment
}
 
type Comment {
  message: String
}

Now, implement the resolver:

export const resolvers = {
  Subscription: {
    newComment: {
      subscribe: () => ps.asyncIterator(Topic.NEW_COMMENT),
    },
  },
};

Calling asyncIterator(topics: string | string[]) will subscribe to the given topics and will return an AsyncIterator binded to the PubSubEngine of graphql-firestore-subscriptions. Everytime, a handler calls the obtained broadcast-function, the PubSubEngine of graphql-firestore-subscriptions will publish the event.

API

createFallThroughHandler

function createFallThroughHandler(
  fs: Firestore,
  overwriteOptions: FallThroughHandlerOptions
): [string, Handler];

Options

Name	Type	Description
topic*	string	-
collection*	string	The firebase collection
transform	TransformStrategy | (change: DocumentChange) => any	Called to transform the broadcast-payload
filter	(change: DocumentChange) => boolean	Called to filter document changes before they are broadcasted

* required

createFallThroughHandlerFromMap

function createFallThroughHandlerFromMap(
  fs: Firestore,
  options: FallThroughHandlerFromMapOptions
): [string, Handler][];

Options

Name	Type	Description
topic	[topic: string]: Object	See createFallThroughHandler#Options for a complete overview

Contribute

Something is broken? The documentation is incorrect? You're missing a feature? ...and you wanna help? That's great.

The following steps are describing the way from an idea / bug / ... to a pull-request.

1. Fork this repository
2. Apply the changes
3. Write tests (you can execute the current tests by calling npm run test:unit OR npm run test:unit:watch)
4. If necessary, update the documentation
5. Open a pull-request
6. 🎉