publish
. For example, this is useful to avoid sending
self-notifications.asyncio.to_thread
or
channels.db.database_sync_to_async
wrappers.subscribe
& publish
) can be
represented both as synchronous or asynchronous (async def
) methods.MySubscription.broadcast()
or
await MySubscription.broadcast()
depending on the context.pip install django-channels-graphql-ws
Create a GraphQL schema using Graphene. Note the MySubscription
class.
import channels_graphql_ws
import graphene
class MySubscription(channels_graphql_ws.Subscription):
"""Simple GraphQL subscription."""
# Leave only latest 64 messages in the server queue.
notification_queue_limit = 64
# Subscription payload.
event = graphene.String()
class Arguments:
"""That is how subscription arguments are defined."""
arg1 = graphene.String()
arg2 = graphene.String()
@staticmethod
def subscribe(root, info, arg1, arg2):
"""Called when user subscribes."""
# Return the list of subscription group names.
return ["group42"]
@staticmethod
def publish(payload, info, arg1, arg2):
"""Called to notify the client."""
# Here `payload` contains the `payload` from the `broadcast()`
# invocation (see below). You can return `None` if you wish to
# suppress the notification to a particular client. For example,
# this allows to avoid notifications for the actions made by
# this particular client.
return MySubscription(event="Something has happened!")
class Query(graphene.ObjectType):
"""Root GraphQL query."""
# Graphene requires at least one field to be present. Check
# Graphene docs to see how to define queries.
value = graphene.String()
async def resolve_value(self):
return "test"
class Mutation(graphene.ObjectType):
"""Root GraphQL mutation."""
# Check Graphene docs to see how to define mutations.
pass
class Subscription(graphene.ObjectType):
"""Root GraphQL subscription."""
my_subscription = MySubscription.Field()
graphql_schema = graphene.Schema(
query=Query,
mutation=Mutation,
subscription=Subscription,
)
Make your own WebSocket consumer subclass and set the schema it serves:
class MyGraphqlWsConsumer(channels_graphql_ws.GraphqlWsConsumer):
"""Channels WebSocket consumer which provides GraphQL API."""
schema = graphql_schema
# Uncomment to send ping message every 42 seconds.
# send_ping_every = 42
# Uncomment to process requests sequentially (useful for tests).
# strict_ordering = True
async def on_connect(self, payload):
"""New client connection handler."""
# You can `raise` from here to reject the connection.
print("New client connected!")
Setup Django Channels routing:
application = channels.routing.ProtocolTypeRouter({
"websocket": channels.routing.URLRouter([
django.urls.path("graphql/", MyGraphqlWsConsumer.as_asgi()),
])
})
Notify﹡ clients when some event happens using
the broadcast()
or broadcast_sync()
method from the OS thread where
there is no running event loop:
MySubscription.broadcast(
# Subscription group to notify clients in.
group="group42",
# Dict delivered to the `publish` method.
payload={},
)
Notify﹡ clients in a coroutine function
with async broadcast()
or broadcast_async()
method:
await MySubscription.broadcast(
# Subscription group to notify clients in.
group="group42",
# Dict delivered to the `publish` method.
payload={},
)
﹡) In case you are testing your client code by notifying it from the Django Shell, you have to setup a channel layer in order for the two instance of your application. The same applies in production with workers.
You should prefer async resolvers and async middleware over sync ones. Async versions will result in faster code execution. To do DB operations you can use Django 4 asynchronous queries.
You can find simple usage example in the example directory.
Run:
cd example/
# Initialize database.
./manage.py migrate
# Create "user" with password "user".
./manage.py createsuperuser
# Run development server.
./manage.py runserver
Play with the API though the GraphiQL browser at http://127.0.0.1:8000.
You can start with the following GraphQL requests:
# Check there are no messages.
query read { history(chatroom: "kittens") { chatroom text sender }}
# Send a message from your session.
mutation send { sendChatMessage(chatroom: "kittens", text: "Hi all!"){ ok }}
# Check there is a message.
query read { history(chatroom: "kittens") { text sender } }
# Open another browser or a new incognito window (to have another
# session cookie) subscribe to make it wait for events.
subscription s { onNewChatMessage(chatroom: "kittens") { text sender }}
# Send another message from the original window and see how subscription
# triggers in the other one.
mutation send { sendChatMessage(chatroom: "kittens", text: "Something ;-)!"){ ok }}
The channels_graphql_ws
module provides the following key classes:
GraphqlWsConsumer
: Django Channels WebSocket consumer which
maintains WebSocket connection with the client.Subscription
: Subclass this to define GraphQL subscription. Very
similar to defining mutations with Graphene. (The class itself is a
"creative" copy of the Graphene Mutation
class.)GraphqlWsClient
: A client for the GraphQL backend. Executes strings
with queries and receives subscription notifications.GraphqlWsTransport
: WebSocket transport interface for the client.GraphqlWsTransportAiohttp
: WebSocket transport implemented on the
AIOHTTP library.For details check the source code which is thoroughly commented. The docstrings of classes are especially useful.
Since the WebSocket handling is based on the Django Channels and subscriptions are implemented in the Graphene-like style it is recommended to have a look the documentation of these great projects:
The implemented WebSocket-based protocol was taken from the library graphql-ws which is used by the Apollo GraphQL. Check the protocol description for details.
NOTE: Prior to 1.0.0rc7 the library used another protocol: subscription-transport-ws (see the protocol description). In fact Apollo GraphQL has been based on this protocol for years, but eventually has switched to a new one, so we did this as well.
The Subscription.broadcast
uses Channels groups to deliver a message
to the Subscription
's publish
method.
ASGI specification
clearly states what can be sent over a channel, and Django models are
not in the list. Since it is common to notify clients about Django
models changes we manually serialize the payload
using
MessagePack
and hack the process to automatically serialize Django models following
the the Django's guide
Serializing Django objects.
strict_ordering
to True
. But note, this disables parallel requests
execution - in other words, the server will not start processing a new
request from the client until it finishes the current one. See
comments in the class GraphqlWsConsumer
. This mode is here primarily
for testing.await
it if so.The context object (info.context
in resolvers) is a SimpleNamespace
instance useful to transfer extra data between GraphQL resolvers. The
lifetime of info.context
corresponds to the lifetime of GraphQL
request, so it does not persist content between different
queries/mutations/subscriptions. It also contains some useful extras:
graphql_operation_id
: The GraphQL operation id came from the client.graphql_operation_name
: The name of GraphQL operation.channels_scope
:
Channels scope.
Contrary to the info.context
, the Channels scope corresponds to the
WebSocket connection not to the GraphQL operation/request.channel_name
: WebSocket channel name.To enable authentication it is typically enough to wrap your ASGI
application into the channels.auth.AuthMiddlewareStack
:
application = channels.routing.ProtocolTypeRouter({
"websocket": channels.auth.AuthMiddlewareStack(
channels.routing.URLRouter([
django.urls.path("graphql/", MyGraphqlWsConsumer),
])
),
})
This gives you a Django user info.context.channels_scope["user"]
in
all the resolvers. To authenticate user you can create a Login
mutation like the following:
class Login(graphene.Mutation, name="LoginPayload"):
"""Login mutation."""
ok = graphene.Boolean(required=True)
class Arguments:
"""Login request arguments."""
username = graphene.String(required=True)
password = graphene.String(required=True)
def mutate(self, info, username, password):
"""Login request."""
# Ask Django to authenticate user.
user = django.contrib.auth.authenticate(username=username, password=password)
if user is None:
return Login(ok=False)
# Use Channels to login, in other words to put proper data to
# the session stored in the scope.
asgiref.sync.async_to_sync(channels.auth.login)(info.context.channels_scope, user)
# Save the session,cause `channels.auth.login` does not do this.
info.context.session.save()
return Login(ok=True)
The authentication is based on the Channels authentication mechanisms. Check the Channels documentation. Also take a look at the example in the example directory.
There is the GraphqlWsClient
which implements GraphQL client working
over the WebSockets. The client needs a transport instance which
communicates with the server. Transport is an implementation of the
GraphqlWsTransport
interface (class must be derived from it). There is
the GraphqlWsTransportAiohttp
which implements the transport on the
AIOHTTP library. Here is an
example:
transport = channels_graphql_ws.GraphqlWsTransportAiohttp(
"ws://backend.endpoint/graphql/", cookies={"sessionid": session_id}
)
client = channels_graphql_ws.GraphqlWsClient(transport)
await client.connect_and_init()
result = await client.execute("query { users { id login email name } }")
users = result["data"]
await client.finalize()
See the GraphqlWsClient
class docstring for the details.
The GraphiQL provided by Graphene doesn't connect to your GraphQL
endpoint via WebSocket; instead you should use a modified GraphiQL
template under graphene/graphiql.html
which will take precedence over
the one of Graphene. One such modified GraphiQL is provided in the
example directory.
To test GraphQL WebSocket API read the appropriate page in the Channels documentation.
In order to simplify unit testing there is a GraphqlWsTransport
implementation based on the Django Channels testing communicator:
channels_graphql_ws.testing.GraphqlWsTransport
. Check its docstring
and take a look at the tests to see how to use it.
The original Apollo's protocol does not allow client to know when a
subscription activates. This inevitably leads to the race conditions on
the client side. Sometimes it is not that crucial, but there are cases
when this leads to serious issues.
Here is the discussion
in the
subscriptions-transport-ws
tracker.
To solve this problem, there is the GraphqlWsConsumer
setting
confirm_subscriptions
which when set to True
will make the consumer
issue an additional next
message which confirms the subscription
activation. Please note, you have to modify the client's code to make it
consume this message, otherwise it will be mistakenly considered as the
first subscription notification.
To customize the confirmation message itself set the GraphqlWsConsumer
setting subscription_confirmation_message
. It must be a dictionary
with two keys "data"
and "errors"
. By default it is set to
{"data": None, "errors": None}
.
It is possible to inject middleware into the GraphQL operation
processing. For that define middleware
setting of your
GraphqlWsConsumer
subclass, like this:
async def threadpool_for_sync_resolvers(next_middleware, root, info, *args, **kwds):
"""Offload synchronous resolvers to the threadpool.
This middleware should always be the last in the middlewares calls
stack and the closest to the real resolver. If this middleware is
not the last it will check the next middleware to call instead of
real resolver. The first middleware in the middlewares list will be
the closest to the resolver.
"""
# Invoke next middleware.
if asyncio.iscoroutinefunction(next_middleware):
result = await next_middleware(root, info, *args, **kwds)
else:
result = await asyncio.to_thread(next_middleware, root, info, *args, **kwds)
return result
class MyGraphqlWsConsumer(channels_graphql_ws.GraphqlWsConsumer):
...
middleware = [threadpool_for_sync_resolvers]
It is recommended to write asynchronous middlewares. But synchronous middlewares are also supported:
def my_middleware(next_middleware, root, info, *args, **kwds):
"""My custom GraphQL middleware."""
# Invoke next middleware.
return next_middleware(root, info, *args, **kwds)
class MyGraphqlWsConsumer(channels_graphql_ws.GraphqlWsConsumer):
...
middleware = [my_middleware]
For more information about GraphQL middleware please take a look at the relevant section in the Graphene documentation.
There is a Tomáš Ehrlich GitHubGist GraphQL Subscription with django-channels which this implementation was initially based on.
There is a promising GraphQL WS library by the Graphene authors. In particular this pull request gives a hope that there will be native Graphene implementation of the WebSocket transport with subscriptions one day.
A reminder of how to setup an environment for the development.
Install PyEnv to be able to work with many Python versions at once PyEnv→Installation.
Install Python versions needed. The command should be executed in the project's directory:
$ pyenv local | xargs -L1 pyenv install
Check that pyenv works correctly. The command:
$ pyenv versions
should show python versions enlisted in
.python-version. If everything is set up
correctly pyenv will switch version of python when you enter and
leave the project's directory. Inside the directory pyenv which python
should show you a python installed in pyenv, outside the dir
it should be the system python.
Install Poetry (https://python-poetry.org/docs/#installation).
$ pipx install poetry
Create local virtualenv in .venv
, install all project dependencies
(from pyproject.toml
) except the project itself.
$ poetry install --no-root
Activate virtualenv There are options:
$ poetry shell
$ source .venv/bin/activate
.venv
with "Python: Select interpreter" and
reopen the terminal.Upgrade Pip:
$ pip install --upgrade pip
Use:
The code is inherently complex because it glues two rather different libraries/frameworks Channels and Graphene. You might need some time to dive into. Here are some quick insights to help you to get on track.
The main classes are GraphqlWsConsumer
and Subscription
. The former
one is a Channels consumer which instantiates each time a WebSocket
connection establishes. User (of the library) subclasses it and tunes
settings in the successor class. The latter is from the Graphene world.
Both classes are tightly coupled. When client subscribes an instance of
GraphqlWsConsumer
subclass holding the WebSocket connection passes to
the Subscription
.
To better dive in it is useful to understand in general terms how
regular request are handled. When server receives JSON from the client,
the GraphqlWsConsumer.receive_json
method is called by Channels
routines. Then the request passes to the _on_gql_subscribe
method
which handles GraphQL message "SUBSCRIBE". Most magic happens there.
A reminder of how to run tests.
$ tox
$ tox -e py38
$ tox -e py310 -- tests/test_basic.py::test_main_usecase
$ poetry run pytest
A reminder of how to make and publish a new release.
poetry version minor
.git tag vX.X.X && git push --tags
.poetry publish --build
.This project is developed and maintained by DATADVANCE LLC. Please submit an issue if you have any questions or want to suggest an improvement.
This work is supported by the Russian Foundation for Basic Research (project No. 15-29-07043).