from django.contrib.auth.models import User

User._meta.get_field('username')._unique = False

class AppUser(User):
    username = models.CharField...
    organization = models.CharField...

from django.contrib.auth.models import AbstractUser
from django.contrib.auth.models import PermissionsMixin

# Custom model for User
class User(AbstractBaseUser, PermissionsMixin):

    first_name = models.CharField(max_length=100, blank=False)
    last_name = models.CharField(max_length=100, blank=True)
    password = models.CharField(max_length=255, blank=False)
    email = models.EmailField(max_length=255, blank=False)
    mobile = models.CharField(max_length=12)
    user_type = models.ForeignKey(UserTypes, on_delete=models.DO_NOTHING)
    is_approved = models.BooleanField(default=False)

    objects = UserManager()
    # Here's the Catch
    USERNAME_FIELD = 'id'

    def get_full_name(self):
        '''
        Returns the first_name plus the last_name, with a space in between.
        '''
        full_name = '%s %s' % (self.first_name, self.last_name)
        return full_name.strip()

    def get_short_name(self):
        '''
        Returns the short name for the user.
        '''
        return self.first_name

    def email_user(self, subject, message, from_email=None, **kwargs):
        '''
        Sends an email to this User.
        '''
        send_mail(subject, message, from_email, [self.email], **kwargs)

    class Meta:
        db_table = 'user'

from django.contrib.auth.base_user import BaseUserManager


class UserManager(BaseUserManager):
    use_in_migrations = True

    def _create_user(self, email, password, **extra_fields):
        """
        Creates and saves a User with the given email and password.
        """
        if not email:
            raise ValueError('The given email must be set')
        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, password=None, **extra_fields):
        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_superuser', 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)