Django signal based on the datetime field value

I'm struggling with the following. I'm trying to create a custom signal that will trigger when the current time will be equal to the value of my model's notify_on DateTimeField.

Something like this:

class Notification(models.Model):
    ...
    notify_on = models.DateTimeField()



def send_email(*args, **kwargs):
    # send email


signals.when_its_time.connect(send_email, sender=User)

After I've read through all docs and I found no information on how to implement such a signal.

Any ideas?

UPDATE: Less naive approach with ability to discard irrelevant tasks: https://stackoverflow.com/a/55337663/9631956

Solution

Ok, thanks to comments by @SergeyPugach I've done the following:

Added a post_save signal that calls a function that adds a task to the celery. apply_async let's you pass eta - estimated time of arrival which can accept DateTimeField directly, that's very convenient.

# models.py
from django.db.models import signals
from django.db import models
from .tasks import send_notification

class Notification(models.Model):
    ...
    notify_on = models.DateTimeField()


def notification_post_save(instance, *args, **kwargs):
    send_notification.apply_async((instance,), eta=instance.notify_on)


signals.post_save.connect(notification_post_save, sender=Notification)

And the actual task in the tasks.py

import logging
from user_api.celery import app
from django.core.mail import send_mail
from django.template.loader import render_to_string


@app.task
def send_notification(self, instance):
    try:
        mail_subject = 'Your notification.'
        message = render_to_string('notify.html', {
            'title': instance.title,
            'content': instance.content
        })
        send_mail(mail_subject, message, recipient_list=[instance.user.email], from_email=None)
    except instance.DoesNotExist:
        logging.warning("Notification does not exist anymore")

I will not get into details of setting up celery, there's plenty of information out there.

Now I will try to figure out how to update the task after it's notification instance was updated, but that's a completely different story.