createsuperuser does not validate usernames that use a UniqueConstraint.

[Lucidiot]

With a custom User model that uses a UniqueConstraint instead of unique=True, the manage.py createsuperuser command does not validate usernames at all.

class CustomUser(AbstractBaseUser):
    custom_username = models.CharField(max_length=255)
    USERNAME_FIELD = 'custom_username'

    class Meta:
        constraints = [
            models.UniqueConstraint(fields=['custom_username'], name='unique_usernames'),
        ]

Running manage.py createsuperuser to create a user with a username that already exists then results in an IntegrityError:

IntegrityError: duplicate key value violates unique constraint "unique_usernames"
DETAIL:  Key (custom_username)=(foo) already exists.

[Mariusz Felisiak]

Thanks for this report. It's ​documented that "The field must be unique (i.e., have unique=True set in its definition)", however I agree that we could improve this, e.g.:

django/contrib/auth/management/commands/createsuperuser.py

@@ -11 +11 @@
 from django.core import exceptions
 from django.core.management.base import BaseCommand, CommandError
 from django.db import DEFAULT_DB_ALIAS
+from django.utils.functional import cached_property
 from django.utils.text import capfirst
 
 
@@ -277 +278 @@
             else "",
         )
 
+    @cached_property
+    def username_is_unique(self):
+        if self.username_field.unique:
+            return True
+        for unique_constraint in self.UserModel._meta.total_unique_constraints:
+            if len(unique_constraint.fields) == 1 and self.username_field.name == unique_constraint.fields[0]:
+                return True
+        return False
+
     def _validate_username(self, username, verbose_field_name, database):
         """Validate username. If invalid, return a string error message."""
-        if self.username_field.unique:
+        if self.username_is_unique:
             try:
                 self.UserModel._default_manager.db_manager(database).get_by_natural_key(
                     username

Would you like to prepare a patch? (a regression test is also required.)

[Lucidiot]

Done: ​PR

Should I update the documentation as well?

[Mariusz Felisiak]

Should I update the documentation as well?

It should be enough to change i.e. to e.g..

[Mariusz Felisiak <felisiak.mariusz@…>]

In 13a9cde1:

Fixed #33613 -- Made createsuperuser detect uniqueness of USERNAME_FIELD when using Meta.constraints.