当用户通过django模型表单注册时，如何为特定类型用户生成自定义id

from django.db.models.signals import pre_save
from django.dispatch import receiver
from django.contrib.auth.models import User

@receiver(pre_save, sender=User)
def generate_custom_id(sender, instance, **kwargs):
    if instance.is_superuser:
        # 为超级用户生成自定义 ID
        instance.custom_id = 'SU-' + str(instance.id)
    elif instance.is_staff:
        # 为员工用户生成自定义 ID
        instance.custom_id = 'ST-' + str(instance.id)
    else:
        # 为普通用户生成自定义 ID
        instance.custom_id = 'USR-' + str(instance.id)

INSTALLED_APPS = [
    ...
    'your_app',
    ...
]

from django.db import models

class UserProfile(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    custom_id = models.CharField(max_length=20, unique=True)