anthbs / graphql-mongoose-subscriptions

graphql-mongoose-subscriptions

This package implements the PubSubEngine Interface from the graphql-subscriptions package and also the new AsyncIterator interface. It allows you to connect your subscriptions manager to a mongoose Pub Sub mechanism to support multiple subscription manager instances.

Installation

At first, install the graphql-mongoose-subscriptions package:

npm install graphql-mongoose-subscriptions

As the graphql-subscriptions package is declared as a peer dependency, you might receive warning about an unmet peer dependency if it's not installed already by one of your other packages. In that case you also need to install it too:

npm install graphql-subscriptions

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 MongoosePubSub instance:

import { MongoosePubSub } from 'graphql-mongoose-subscriptions';
const pubsub = new MongoosePubSub();

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 MongoosePubSub instance will send mongoose a SUBSCRIBE message to the topic provided and will return an AsyncIterator binded to the MongoosePubSub 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 MongoosePubSub will PUBLISH the event over mongoose 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 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 a pattern on subscription

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

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 mongoose Client

The basic usage is great for development and you will be able to connect to a mongoose server running on your system seamlessly. For production usage, it is recommended to send a mongoose client from the using code and pass in any options you would like to use. e.g: Connection retry strategy.

import { MongoosePubSub } from 'graphql-mongoose-subscriptions';
import mongoose from 'mongoose'; 

const mongoose = require('mongoose');
mongoose.connect('mongodb://localhost:27017/test', {useNewUrlParser: true, useUnifiedTopology: true});
const pubsub = new MongoosePubSub();

const pubsub = new MongoosePubSub({mongooseOptions:{url:'mongodb://localhost:27017/test',options:{useNewUrlParser: true, useUnifiedTopology: true}}})