Create OneToOne instance on model creation

Question

I'm building my first django app. I have a user, and the user has a list of favourites. A user has exactly one list of favourites, and that list belongs exclusively to that user.

class User(models.Model):     name = models.CharField(max_length=200)  class FavouriteList(models.Model):     user = models.OneToOneField(User)     favourites = models.ManyToManyField(Favourite, blank=True) 

When a new user is created, I want to ensure that the user has a FavouriteList. I've looked around in the Django documentation and haven't had much luck.

Does anyone know how I can ensure that a model has a child object (e.g. FavouriteList) when it is created?

Answer 1

The most common way to accomplish this is to use the Django signals system. You can attach a signal handler (just a function somewhere) to the post_save signal for the User model, and create your favorites list inside of that callback.

from django.db.models.signals import post_save from django.dispatch import receiver from django.contrib.auth.models import User  @receiver(post_save, sender=User) def create_favorites(sender, instance, created, **kwargs):     if created:         Favorites.objects.create(user=instance) 

The above was adapted from the Django signals docs. Be sure to read the signals docs entirely because there are a few issues that can snag you such as where your signal handler code should live and how to avoid duplicate handlers.