Django - how to automatically create a new model instance when another model instance is created

Question

I have an Order and Notification Model, whenever there is a new order model instance, i want to immediately create a notification for the new order, i wrote some functions in the models but when there is a new order, the notification instance does not get created. i still think there should be a better way to do this, how can i go about this?

models.py


class Orders(models.Model):
    service = models.ForeignKey(Service, on_delete=models.SET_NULL, null=True, related_name="service_orders")
    seller = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, related_name="seller")

    def create_notification(self):
        create_notification = Notification.objects.create(provider=self.seller, service=self.service, order=self , notification_type='new_order')
        create_notification.save()
        return create_notification



class Notification(models.Model):
    provider = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, related_name="provider_notifications")
    service = models.ForeignKey(Service, on_delete=models.SET_NULL, null=True, related_name="service_notifications")
    order = models.ForeignKey(Orders, on_delete=models.SET_NULL, null=True, related_name="service_order")
    notification_type = models.CharField(max_length=100, choices=NOTIFICATION_TYPE, default="none")

Where are u calling the create_notification function?

Lax_Sam
– Lax_Sam

2023-02-11 04:47:12 +00:00
Commented Feb 11, 2023 at 4:47 — Lax_Sam
– Lax_Sam, Commented Feb 11, 2023 at 4:47

allexiusw · Accepted Answer · 2023-02-11 05:41:15Z

You need to do something like the following:

class Orders(models.Model):
    service = models.ForeignKey(Service, on_delete=models.SET_NULL, null=True, related_name="service_orders")
    seller = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, related_name="seller")

    def create_notification(self):
        create_notification = Notification.objects.create(
            provider=self.seller, service=self.service, order=self , notification_type='new_order')
        create_notification.save()
        return create_notification

    def save(self, force_insert=False, force_update=False, using=None, update_fields=None):
        super().save(force_insert=force_insert, force_update=force_update, using=using, update_fields=update_fields)
        self.create_notification()

Where save method will be overwriten and once you persist it in the database layer then you can safety call the method create_notification.

Best way to achieve it could be using signals to decouple the logic from the model and manage it in a separate business logic component, but if you don't mind applying the best practices you are good to go with the solution.

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