Graphene Subscriptions

A plug-and-play GraphQL subscription implementation for Graphene + Django built using Django Channels. Provides support for model creation, mutation and deletion subscriptions out of the box.

Installation

1. Install graphene-subscriptions

   $ pip install graphene-subscriptions

2. Add graphene_subscriptions to INSTALLED_APPS:

   # your_project/settings.py
   INSTALLED_APPS = [
       # ...
       'graphene_subscriptions'
   ]

3. Add Django Channels to your project (see: Django Channels installation docs) and set up Channel Layers. If you don't want to set up a Redis instance in your dev environment yet, you can use the in-memory Channel Layer:

   # your_project/settings.py
   CHANNEL_LAYERS = {
       "default": {
           "BACKEND": "channels.layers.InMemoryChannelLayer"
       }
   }

4. Add GraphqlSubscriptionConsumer to your routing.py file.

   # your_project/routing.py
   from channels.routing import ProtocolTypeRouter, URLRouter
   from django.urls import path 
   
   from graphene_subscriptions.consumers import GraphqlSubscriptionConsumer
   
   application = ProtocolTypeRouter({
       "websocket": URLRouter([
           path('graphql/', GraphqlSubscriptionConsumer)
       ]),
   })

5. Connect signals for any models you want to create subscriptions for

   # your_app/signals.py
   from django.db.models.signals import post_save, post_delete
   from graphene_subscriptions.signals import post_save_subscription, post_delete_subscription
   
   from your_app.models import YourModel
   
   post_save.connect(post_save_subscription, sender=YourModel, dispatch_uid="your_model_post_save")
   post_delete.connect(post_delete_subscription, sender=YourModel, dispatch_uid="your_model_post_delete")
   
   # your_app/apps.py
   from django.apps import AppConfig
   
   class YourAppConfig(AppConfig):
       name = 'your_app'
   
       def ready(self):
           import your_app.signals

6. Define your subscriptions and connect them to your project schema

   #your_project/schema.py
   import graphene
   
   from your_app.graphql.subscriptions import YourSubscription
   
   
   class Query(graphene.ObjectType):
       base = graphene.String()
   
   
   class Subscription(YourSubscription):
       pass
   
   
   schema = graphene.Schema(
       query=Query,
       subscription=Subscription
   )

Defining Subscriptions

Subscriptions in Graphene are defined as normal ObjectType's. Each subscription field resolver must return an observable which emits values matching the field's type.

A simple hello world subscription (which returns the value "hello world!" every 3 seconds) could be defined as follows:

import graphene
from rx import Observable

class Subscription(graphene.ObjectType):
    hello = graphene.String()

    def resolve_hello(root, info):
        return Observable.interval(3000) \
                         .map(lambda i: "hello world!")

Responding to Model Events

Each subscription that you define will receive a an Observable of SubscriptionEvent's as the root parameter, which will emit a new SubscriptionEvent each time one of the connected signals are fired.

A SubscriptionEvent has two attributes: the operation that triggered the event, usually CREATED, UPDATED or DELETED) and the instance that triggered the signal.

Since root is an Observable, you can apply any rxpy operations before returning it.

Model Created Subscriptions

For example, let's create a subscription called yourModelCreated that will be fired whenever an instance of YourModel is created. Since root receives a new event every time a connected signal is fired, we'll need to filter for only the events we want. In this case, we want all events where operation is created and the event instance is an instance of our model.

import graphene
from graphene_django.types import DjangoObjectType
from graphene_subscriptions.events import CREATED

from your_app.models import YourModel


class YourModelType(DjangoObjectType)
    class Meta:
        model = YourModel


class Subscription(graphene.ObjectType):
    your_model_created = graphene.Field(YourModelType)

    def resolve_your_model_created(root, info):
        return root.filter(
            lambda event:
                event.operation == CREATED and
                isinstance(event.instance, YourModel)
        ).map(lambda event: event.instance)

Model Updated Subscriptions

You can also filter events based on a subscription's arguments. For example, here's a subscription that fires whenever a model is updated:

import graphene
from graphene_django.types import DjangoObjectType
from graphene_subscriptions.events import UPDATED 

from your_app.models import YourModel


class YourModelType(DjangoObjectType)
    class Meta:
        model = YourModel


class Subscription(graphene.ObjectType):
    your_model_updated = graphene.Field(YourModelType, id=graphene.ID())

    def resolve_your_model_updated(root, info, id):
        return root.filter(
            lambda event:
                event.operation == UPDATED and
                isinstance(event.instance, YourModel) and
                event.instance.pk == int(id)
        ).map(lambda event: event.instance)

Model Updated Subscriptions

Defining a subscription that is fired whenever a given model instance is deleted can be accomplished like so

import graphene
from graphene_django.types import DjangoObjectType
from graphene_subscriptions.events import DELETED 

from your_app.models import YourModel


class YourModelType(DjangoObjectType)
    class Meta:
        model = YourModel


class Subscription(graphene.ObjectType):
    your_model_deleted = graphene.Field(YourModelType, id=graphene.ID())

    def resolve_your_model_deleted(root, info, id):
        return root.filter(
            lambda event:
                event.operation == DELETED and
                isinstance(event.instance, YourModel) and
                event.instance.pk == int(id)
        ).map(lambda event: event.instance)

Custom Events

Sometimes you need to create subscriptions which responds to events other than Django signals. In this case, you can use the SubscriptionEvent class directly. (Note: in order to maintain compatibility with Django channels, all instance values must be json serializable)

For example, a custom event subscription might look like this:

import graphene

CUSTOM_EVENT = 'custom_event'

class CustomEventSubscription(graphene.ObjectType):
    custom_subscription = graphene.Field(CustomType)

    def resolve_custom_subscription(root, info):
        return root.filter(
            lambda event:
                event.operation == CUSTOM_EVENT
        ).map(lambda event: event.instance)


# elsewhere in your app:
from graphene_subscriptions.events import SubscriptionEvent

event = SubscriptionEvent(
    operation=CUSTOM_EVENT,
    instance=<any json-serializable value>
)

event.send()

Production Readiness

This implementation was spun out of an internal implementation I developed which we've been using in production for the past 6 months at Jetpack. We've had relatively few issues with it, and I am confident that it can be reliably used in production environments.

However, being a startup, our definition of production-readiness may be slightly different from your own. Also keep in mind that the scale at which we operate hasn't been taxing enough to illuminate where the scaling bottlenecks in this implementation may hide.

If you end up running this in production, please reach out and let me know!

Contributing

PRs and other contributions are very welcome! To set up graphene_subscriptions in a development envrionment, do the following:

1. Clone the repo

   $ git clone git@github.com:jaydenwindle/graphene-subscriptions.git

2. Install poetry

   $ curl -sSL https://raw.githubusercontent.com/sdispater/poetry/master/get-poetry.py | python

3. Install dependencies

   $ poetry install

4. Run the test suite

   $ poetry run pytest