Foreign key default value in django model

Question

I'm starting an app with django; i love it so far but i've trouble initializing my database. To sum up, i need a table user and a table role; a user has a FK to role. Upon creation a user must have this role set explicitly or defaulting to a default role 'Regular user'.

I could create the model without the database, then manually create the role, then add the default and migrate; but that does not look nice; I tried adding to the database in-between the two models definition but obviously it does not work as the tables are not created during the makemigration command.

Is there any way to achieve what I want? Here is my current models if it helps; feel free to report any non-sense in this; i'm learning. Thx;)

from django.db import models


class Role(models.Model):
    name = models.CharField(max_length=100)
    identifier = models.CharField(max_length=20)
    ts_create = models.DateTimeField(auto_now_add=True)
    ts_update = models.DateTimeField(auto_now=True, default=None, null=True)

    def __str__(self):
        return self.name


userRole = Role.objects.get_or_create(name="Regular user", identifier="USER")
adminRole = Role.objects.get_or_create(name="Administrator", identifier="ADMIN")
ownerRole = Role.objects.get_or_create(name="Owner", identifier="OWNER")


class User(models.Model):
    username = models.CharField(max_length=100, unique=True)
    user_type = models.ForeignKey(Role, related_name="user_type", on_delete=models.PROTECT, default=userRole)
    roles = models.ManyToManyField(Role, related_name="roles", db_table="core_roles_assignations")
    ts_create = models.DateTimeField(auto_now_add=True)
    ts_update = models.DateTimeField(auto_now=True, default=None, null=True)

    def __str__(self):
        return self.username

    def is_admin(self):
        return self.user_type.identifier == "ADMIN"


owner = User.objects.get_or_create(username="Nindouja", user_role=Role.objects.first())

``` python

Answer 1

You can try Signal for save role when User created. https://docs.djangoproject.com/en/3.1/ref/signals/

Ideal is: when user created, check user have role or not. If dont have, add default role for it. It will work everytime you try create user. Example:

@receiver(post_save, sender= User)
def post_save_user(sender, instance, created, **kwargs):
    if created:
        roles = instance.roles.all() # check user have any roles
        if not roles:
            default_role = Role.objects.first()
            instance.roles.add(default_role)

Answer 2

If you need inital data with your db, you can use dumpdata and loaddata .

Dumpdata(Use only during the first time, after manually adding the roles to the db)

mkdir myapp/fixtures
python manage.py dumpdata myapp --indent=2 --output=myapp/fixtures/
mydata.json

When you are migrating, you can use:

Loaddata

$  python manage.py migrate myapp && python manage.py loaddata mydata.json