如何在 Django 中添加另一个模型的模型对象时自动创建一个模型的模型对象

Question

Say for example I have a Model called Player. I want Model objects of Player created when new Users are added in django (from django.contrib.auth.models.User ) such that each User object in User model has its own object in Player model. I know that I would technically have to use models.ForeignKey() to create a field in Player model and relate it to the User model and that I don't have to worry about deletion of users if I use the on_delete=models.CASCADE parameter in models.ForeignKey() but how do I automatically create these objects with like default values and such. Initially this was my code to do so:

for name in User.objects.all().values_list('username', flat=True):
if name not in Player.objects.all().values_list('player_name', flat=True):
    new_player = Player(player_name=name, current_level_no=None, no_of_moves=None)
    new_player.save()
else:
    pass

But this would give me a DatabaseIntegrityError that "Models aren't loaded yet". So I am confused about what to do or how to go forward.

As always, I greatly appreciate all answers!

Answer 1

Check out Django signals , specifically the post_save signal . Essentially, Django lets you define a function that will be run whenever your User model is saved. You'd use it something like this:

from django.db.models.signals import post_save

def create_player(sender, instance, created, **kwargs):
    if created:
        Player.objects.create(user=instance)  # instance is the User object

post_save.connect(create_player, sender=User)

Note that if you already have User objects in your database, this won't create Player objects for them; you'll want to do that by running a loop similar to the one you posted in the Django shell (using python manage.py shell ). The signal will run on every subsequent save of a user model.