[Django]-Unique together in Django User Model

AbstractUser is a mostly-complete model that defines a set of default fields, including username uniqueness. If that doesn’t work for you, then you should inherit from AbstractBaseUser instead and define the full set of fields.

Uniqueness on the username field is only if you use the built-in authentication backend.

Directly from the django docs

If you use the default authentication backend, then your model must have a single unique field…A non-unique username field is allowed if you use a custom authentication backend that can support it.

Django Custom Authentication

Hope this helps

From your question and the comments its pretty clear(if i am not fully misunderstood) that you want to save an user with an email (an identifier) with multiple platform. If this is the case, you can use a postgres ArrayField on your platform column if your database is Postgresql, or alternavely you can use JsonField provided by django.

1. Postgresql Array Field available in django > 1.7

2. Django Json Field

I might be too late to answer this but the solution I used recently for the same problem is:

class User(AbstractUser):
    platform_and_email = models.CharField(max_length=100, unique=True)
    username = models.CharField(max_length=20, blank=True, null=True)
    email = models.EmailField(_('email address'), unique=True)

    USERNAME_FIELD = 'platform_and_email'
    REQUIRED_FIELDS = ['username', 'first_name', 'last_name']

    class Meta:
        verbose_name = "App User"
        verbose_name_plural = "App Users"

You can use a single field and set it as unique. On the client side of your app you can authenticate user by doing ‘platform_’ + email behind the scenes.

You will also have to write your own custom backend and make it use your platform_and_email field to validate and authenticate.

Let me know if you need more explanation on this.