How can I make SSE with Python (Django)?

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I have two different pages, one (A) that displays data taken from a model object, and one (B) that changes its fields. I would like that when the post data is sent from B to

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没有蜡笔的小新

2020-12-17 22:13

This is working example from w3schools in Django:

template

<!DOCTYPE html>
<html>
<body>

<h1>Getting server updates</h1>
<div id="result"></div>

<script>
if(typeof(EventSource) !== "undefined") {
  var source = new EventSource("stream/");
  source.onmessage = function(event) {
    document.getElementById("result").innerHTML += event.data + "<br>";
  };
} else {
  document.getElementById("result").innerHTML = "Sorry, your browser does not support server-sent events...";
}
</script>

</body>
</html>

views

import datetime
import time
from django.http import StreamingHttpResponse

def stream(request):
    def event_stream():
        while True:
            time.sleep(3)
            yield 'data: The server time is: %s\n\n' % datetime.datetime.now()
    return StreamingHttpResponse(event_stream(), content_type='text/event-stream')

urls

urlpatterns = [
    path('stream/', views.stream, name='stream')
]

Update:

If you want to manage your notifications you can create the model like:

from django.db import models

class Notification(models.Model):
    text = models.CharField(max_length=200)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    sent = models.BooleanField(default=False)

Then create the view that is looking for the first unsent notification and sends it:

@login_required
def stream(request):
    def event_stream():
        while True:
            time.sleep(3)
            notification = Notification.objects.filter(
                sent=False, user=request.user
            ).first()

            text = ''

            if notification:
                text = notification.text
                notification.sent = True
                notification.save()

            yield 'data: %s\n\n' % text

    return StreamingHttpResponse(event_stream(), content_type='text/event-stream')

And the send_notification function that creates an entry in the Notification model (just call this function from anywhere in your code):

def send_notification(user, text):
    Notification.objects.create(
        user=user, text=text
    )

That's it, simple as that.

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猫巷女王i

2020-12-17 22:22

After reading this, I think I understood the whole thing (please comment if I’m wrong).  

Django does NOT natively support keep-alive connections.  This means, when the client gets the message from the server, the connection is immediately closed after (like any classic HTTP request/response cycle).

 What’s different with text/event-stream request, is that the client automatically tries to reconnect to the server every second (the length can be changed with a retry parameter).  

Unfortunately, it seems using SSE in that case has no interest since it has the same con’s that polling (ie. a request/response cycle occurs each X seconds).

  As expected and mentioned in other answers, I would need django-channels to create a persistent connection that prevent HTTP request/response overheads and ensure the message is sent immediately. 

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