Django - Changing Auth username to Autofield breaks the code

I've an application where I need to change username field to Autofield.

Use-case - I'am building an application where when the users will be created, usernames should be like CustomerID(integers) in banking applications.

There are 2 ways of doing it:-

1) Have an id (PK), the default implementation of it. Copy the id, of the object and assign it to the username column, to allow users to sign-in via the id. Trade-offs

Two duplicate columns.
How would I call create_user function as it requires username.

2) Allow login via the IDs, update AuthBackend and allow login via the IDs too. TradeOff

What will be the value of the username. Shall I keep it as email?
Not sure, whether allowing login via the IDs is a good idea.

Pheww, enough of discussion. Now comes the implementation(problematic) part.:-

Here's my model.

 class User(AbstractUser):
    username = models.BigAutoField(primary_key=True)
    user_id = models.UUIDField(default=uuid.uuid4, unique=True,
                               editable=False)

A model can't have more than one AutoField, as a result, username is PK.

I migrations worked perfectly well. And the table was created.

However, when I create a user using

User.objects.create_user(email=email, password=password)  #expecting the username to be auto-generated.

It says username is mandatory.

I checked Django code UserManager function create_user, and updated argument username=None

class CustomUserManager(UserManager):
    use_in_migrations = True

    def create_user(self, username=None, email=None, password=None,
                    **extra_fields):
        return super(CustomUserManager, self).create_user(username=username,
                                                          email=email,
                                                          password=password,
                                                          extra_fields=extra_fields)

It still throws an exception:-

In [4]: User.objects.create_user(email='[email protected]', password='abcd1234@')
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-4-de9c49dd635d> in <module>()
----> 1 User.objects.create_user(email='[email protected]', password='abcd1234@')

/Users/praful/Desktop/code/seynse/authentication/app/modules/users/models.py in create_user(self, username, email, password, **extra_fields)
     17                                                           email=email,
     18                                                           password=password,
---> 19                                                           extra_fields=extra_fields)
     20
     21

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/contrib/auth/models.py in create_user(self, username, email, password, **extra_fields)
    157         extra_fields.setdefault('is_staff', False)
    158         extra_fields.setdefault('is_superuser', False)
--> 159         return self._create_user(username, email, password, **extra_fields)
    160
    161     def create_superuser(self, username, email, password, **extra_fields):

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/contrib/auth/models.py in _create_user(self, username, email, password, **extra_fields)
    146         """
    147         if not username:
--> 148             raise ValueError('The given username must be set')
    149         email = self.normalize_email(email)
    150         username = self.model.normalize_username(username)

ValueError: The given username must be set

What can be done in this case? How can I change username to AutoField.

You must create a custom manager for your user model. It can inherit from BaseManager, but not from the default UserManager:

class CustomUserManager(BaseUserManager):
    use_in_migrations = True

    def _create_user(self, email, password, **extra_fields):
        """
        Create and save a user with the given email, and password.
        """
        email = self.normalize_email(email)
        user = self.model(email=email, **extra_fields)
        user.set_password(password)
        user.save(using=self._db)
        return user

    def create_user(self, email=None, password=None, **extra_fields):
        extra_fields.setdefault('is_staff', False)
        extra_fields.setdefault('is_superuser', False)
        return self._create_user(email, password, **extra_fields)

    def create_superuser(self, email, password, **extra_fields):
        extra_fields.setdefault('is_staff', True)
        extra_fields.setdefault('is_superuser', True)

        if extra_fields.get('is_staff') is not True:
            raise ValueError('Superuser must have is_staff=True.')
        if extra_fields.get('is_superuser') is not True:
            raise ValueError('Superuser must have is_superuser=True.')

        return self._create_user(email, password, **extra_fields)


class User(AbstractUser):
    username = models.BigAutoField(primary_key=True)
    user_id = models.UUIDField(default=uuid.uuid4, unique=True,
                               editable=False)

    objects = CustomUserManager()

    def __str__(self):
        return str(self.username)

Note that I've completely removed username, as it doesn't make sense to pass an explicit value for an AutoField.

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