UserRole model with user is assigned when the instance is save

models.py

from django.contrib.auth.models import User
from django.db import models

from poinkbackend.apps.commons.models import AbstractTimestamp
from poinkbackend.apps.roles.models import Role


class UserRole(AbstractTimestamp):
    user = models.ForeignKey(User, related_name='user_roles', on_delete=models.PROTECT)
    role = models.ForeignKey(Role, related_name='user_roles', on_delete=models.PROTECT)

    def __str__(self):
        return f'{self.user}-{self.role}'

    def save(self, force_insert=False, force_update=False, using=None,
             update_fields=None):
        instance = super().save(force_insert=False, force_update=False, using=None,
                                update_fields=None)
        self.user.groups.add(self.role.group)
        return instance

    def delete(self, using=None, keep_parents=False):
        self.user.groups.remove(self.role.group)
        return super().delete(using=None, keep_parents=False)