我在account.models.py中的自定义用户模型：

class MyRegistration(AbstractBaseUser, PermissionsMixin):
    location_list=[
        ('abc', 'abc'),
        ('def', 'def'),
        ]
    username=models.CharField(max_length=10, unique=True)
    email=models.EmailField(unique=True)
    first_name=models.CharField(max_length=150)
    last_name=models.CharField(max_length=150)
    location=models.CharField(max_length=10, choices=location_list, default=None)
    designation=models.CharField(max_length=70)
    is_active=models.BooleanField()
    is_staff=models.BooleanField(default=False)
    start_date=models.DateTimeField(default=timezone.now)
    last_login=models.DateTimeField(null=True)

    USERNAME_FIELD='username'
    REQUIRED_FIELDS=['email', 'first_name', 'last_name', 'location', 'designation']
    objects=FirstManager()
    def __str__(self):
        return self.username

sample.models.py中的模型：

class LockData(models.Model):
    patient=models.ForeignKey(Patient, on_delete=CASCADE, default=None)
    patient_type=models.ForeignKey(PatientType, on_delete=CASCADE, default=None, blank=True, null=True)
    lock=models.BooleanField(default=False)
    date=models.DateField(default=datetime.date.today)
    created_on=models.DateTimeField(auto_now_add=True)
    modified_on=models.DateTimeField(auto_now=True)

因此，除了created_on和modified_on字段外，我还需要'created_by'和'modified_by'字段。