Make it easier to extend UserCreationForm for custom user models

[Baptiste Mispelon]

The documentation ​states that UserCreationForm must be re-written when using a custom user model.

However, for simple subclasses of AbstractUser it's actually simpler to extend (rather than rewrite) the existing form like so:

class CustomUserCreationForm(UserCreationForm):
    class Meta(UserCreationForm.Meta):
        model = CustomUser

Unfortunately, this fails because the clean_username method of UserCreationForm still references the original User model directly (this technique works with UserChangeForm though).
To get it working, the original clean_username method needs to be copied over and modified to use the custom user model, like so:

class CustomUserCreationForm(UserCreationForm):
    class Meta(UserCreationForm.Meta):
        model = CustomUser

    def clean_username(self):
        username = self.cleaned_data["username"]
        try:
            CustomUser.objects.get(username=username)
        except CustomUser.DoesNotExist:
            return username
        raise forms.ValidationError(self.error_messages['duplicate_username'])

This works, but having to copy/paste some code is not a very good practice.

Therefore, I propose to change UserCreationForm.clean_username to use Meta.model instead of User.

This allows the creation of custom user creation forms by simply redefining the user model in the form's Meta class (like in the first example).

The documentation could also be extended to show an example of how to extend the builtin auth forms that require it.

[Russell Keith-Magee]

Seems like a reasonable idea to me. Patch needs a documentation update to point out the changed constraints on form usage.

[Baptiste Mispelon]

I've updated the patch with some documentation.

I've also started a branch on my fork: ​https://github.com/bmispelon/django/tree/ticket-19353

The wording on the documentation feels a bit awkward and I'd appreciate comments and ideas to improve it.

[wiz]

On a related note, i've added some fields to my subclass of AbstractUser and admin fieldset setting now complains about missing fields from the [change] form. The fix is to use get_user_model() in Meta too.

[rpedigoni]

Replying to bmispelon:

I've updated the patch with some documentation.

I've also started a branch on my fork: ​https://github.com/bmispelon/django/tree/ticket-19353

The wording on the documentation feels a bit awkward and I'd appreciate comments and ideas to improve it.

I just made a similar fix and right before sending a pull request I found your ticket :)
Could submit a pull request?

Also, I left a comment on your branch about the username field: ​https://github.com/bmispelon/django/commit/81c9bd6a2a55a8cf1c2bee351db873ea7403db1e#commitcomment-2507426

[Victor Hooi]

Hi,
Curious - what is the status on this ticket?
Are there still blockers on it being accepted?
Cheers,
Victor

[Dominic Rodger]

I ran into this problem today, and was very confused (the stack trace you get when this goes wrong doesn't lead you quickly to where the problem occurred). The patch looks reasonable to me - it's got tests, docs, and a simple enough implementation. Is there anything we can do to get it committed? I'm more than happy to do any additional work here if it'd help, if Baptiste doesn't have time to work on it at the moment.

[Tim Graham]

This should be easier after removing some of the logic from the form in #13147.

[Loic Bistuer <loic.bistuer@…>]

In 671e0c937c112b1908048b4d8deb14c0116b8946:

Further fix the release notes for refs #13147.

Mention of custom user models has been removed since UserCreationForm
didn't support custom user models anyway. Refs #19353.

[Berker Peksag]

Since 849538d03df21b69f0754a38ee4ec5f48fa02c52 has been committed, I think UserCreationForm works well with subclasses of AbstractUser. Here is a test case:

diff --git a/tests/auth_tests/test_forms.py b/tests/auth_tests/test_forms.py
index aa0a6af..68a1b88 100644
--- a/tests/auth_tests/test_forms.py
+++ b/tests/auth_tests/test_forms.py
@@ -10,6 +10,7 @@ from django.contrib.auth.forms import (
     SetPasswordForm, UserChangeForm, UserCreationForm,
 )
 from django.contrib.auth.models import User
+from django.contrib.auth.tests.custom_user import ExtensionUser
 from django.contrib.sites.models import Site
 from django.core import mail
 from django.core.mail import EmailMultiAlternatives
@@ -153,6 +154,20 @@ class UserCreationFormTest(TestDataMixin, TestCase):
             form['password2'].errors
         )
 
+    def test_custom_form(self):
+        class CustomUserCreationForm(UserCreationForm):
+            class Meta(UserCreationForm.Meta):
+                model = ExtensionUser
+                fields = UserCreationForm.Meta.fields + ('date_of_birth',)
+
+        data = {
+            'username': 'testclient',
+            'password1': 'testclient',
+            'password2': 'testclient',
+            'date_of_birth': '1988-02-24',
+        }
+        form = CustomUserCreationForm(data)
+        self.assertTrue(form.is_valid())
 
 @override_settings(USE_TZ=False, PASSWORD_HASHERS=['django.contrib.auth.hashers.SHA1PasswordHasher'])
 class AuthenticationFormTest(TestDataMixin, TestCase):

I can send this as a PR, if it looks reasonable.

[Tim Graham]

Sure, might want to also consider including some documentation updates from bmispelon's branch in comment 5.

[Baptiste Mispelon]

I'm also curious to see if UserChangeForm can now also be used.

FYI, the documentation moved to ​https://docs.djangoproject.com/en/dev/topics/auth/customizing/#custom-users-and-the-built-in-auth-forms since the original ticket was opened.

Thanks.

[Berker Peksag]

Pull request: ​https://github.com/django/django/pull/6142

• Converted my test in comment 16 to an actual test case
• Added a test for UserChangeForm
• Ported documentation updates from bmispelon's branch in comment 5

[Tim Graham <timograham@…>]

In f0425c7:

Refs #19353 -- Added tests for using custom user models with built-in auth forms.

Also updated topics/auth/customizing.txt to reflect that subclasses of
UserCreationForm and UserChangeForm can be used with custom user models.

Thanks Baptiste Mispelon for the initial documentation.

[Tim Graham <timograham@…>]

In f78892f2:

[1.9.x] Refs #19353 -- Added tests for using custom user models with built-in auth forms.

Also updated topics/auth/customizing.txt to reflect that subclasses of
UserCreationForm and UserChangeForm can be used with custom user models.

Thanks Baptiste Mispelon for the initial documentation.

Backport of f0425c72601f466c6a71518749c6d15b94945514 from master

[Tim Graham]

If there are any further improvements, let's open a new ticket. Thanks!