Sending a message to a single user using django-channels

Question

I have been trying out django-channels including reading the docs and playing around with the examples.

I want to be able to send a message to a single user that is triggered by saving a new instance to a database.

My use case is creating a new notification (via a celery task) and once the notification has saved, sending this notification to a single user.

This sounds like it is possible (from the django-channels docs)

...the crucial part is that you can run code (and so send on channels) in response to any event - and that includes ones you create. You can trigger on model saves, on other incoming messages, or from code paths inside views and forms.

However reading the docs further and playing around with the django-channels examples, I can't see how I can do this. The databinding and liveblog examples demonstrate sending to a group, but I can't see how to just send to a single user.

Answer 1

Little update since Groups work differently with channels 2 than they did with channels 1. There is no Group class anymore, as mentioned here.

The new groups API is documented here. See also here.

What works for me is:

# Required for channel communication
from channels.layers import get_channel_layer
from asgiref.sync import async_to_sync


def send_channel_message(group_name, message):
    channel_layer = get_channel_layer()
    async_to_sync(channel_layer.group_send)(
        '{}'.format(group_name),
        {
            'type': 'channel_message',
            'message': message
        }
    )

Do not forget to define a method to handle the message type in the Consumer!

    # Receive message from the group
    def channel_message(self, event):
        message = event['message']

        # Send message to WebSocket
        self.send(text_data=json.dumps({
            'message': message
        }))