Value error on related user name during save of user model

[Axel Rau]

problem:
While upgrading from 1.9 to 1.11, ForwardManyToOneDescriptor.set()
tries to assign a string (description of the related instance) to the related user name field
of user model.
diagnosis:
In 1.10 normalize_username(), a class method of AbstractBaseUser, has been introduced.
This class method forces the related user name instance to a string.
Fix:
Overwriting this with a method which just returns the 'username' fixes the problem.

Details:

class AbstractEmailUser(AbstractBaseUser, PermissionsMixin, FieldlistForDetailTemplateMixin):

localemail = models.OneToOneField('Mailbox', verbose_name=_('Local E-mail'),

related_name='localemail', db_column='localemail',
editable=('UR', 'UE', 'UL'))

objects = UserManager()

USERNAME_FIELD = 'localemail'
REQUIRED_FIELDS = []

class Meta:

abstract = True
ordering = localemail

def get_username(self):

return getattr(self, self.USERNAME_FIELD)

class Mailbox(models.Model):

id = models.AutoField(primary_key=True)
localpart = models.CharField(_('Localpart'), max_length=40)
localdomainfk = models.ForeignKey(Localdomain, verbose_name=_('Domain'), db_column='localdomainfk', editable=('AL',))

…

def str(self):

return self.localpart+ '@'+self.localdomainfk.name

Internal Server Error: /admin/erdb/account/19/change/
Traceback (most recent call last):

File "...python3.5/site-packages/django/core/handlers/exception.py", line 41, in inner

response = get_response(request)

File "...python3.5/site-packages/django/core/handlers/base.py", line 249, in _legacy_get_response

response = self._get_response(request)

File "...python3.5/site-packages/django/core/handlers/base.py", line 187, in _get_response

response = self.process_exception_by_middleware(e, request)

File "...python3.5/site-packages/django/core/handlers/base.py", line 185, in _get_response

response = wrapped_callback(request, *callback_args, callback_kwargs)

File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/contextlib.py", line 30, in inner

return func(*args, kwds)

File "...python3.5/site-packages/django/contrib/admin/options.py", line 551, in wrapper

return self.admin_site.admin_view(view)(*args, kwargs)

File "...python3.5/site-packages/django/utils/decorators.py", line 149, in _wrapped_view

response = view_func(request, *args, kwargs)

File "...python3.5/site-packages/django/views/decorators/cache.py", line 57, in _wrapped_view_func

response = view_func(request, *args, kwargs)

File "...python3.5/site-packages/django/contrib/admin/sites.py", line 224, in inner

return view(request, *args, kwargs)

File "...python3.5/site-packages/django/contrib/admin/options.py", line 1511, in change_view

return self.changeform_view(request, object_id, form_url, extra_context)

File "...python3.5/site-packages/django/utils/decorators.py", line 67, in _wrapper

return bound_func(*args, kwargs)

File "...python3.5/site-packages/django/utils/decorators.py", line 149, in _wrapped_view

response = view_func(request, *args, kwargs)

File "...python3.5/site-packages/django/utils/decorators.py", line 63, in bound_func

return func.get(self, type(self))(*args2, kwargs2)

File "...python3.5/site-packages/django/contrib/admin/options.py", line 1408, in changeform_view

return self._changeform_view(request, object_id, form_url, extra_context)

File "...python3.5/site-packages/django/contrib/admin/options.py", line 1440, in _changeform_view

if form.is_valid():

File "...python3.5/site-packages/django/forms/forms.py", line 183, in is_valid

return self.is_bound and not self.errors

File "...python3.5/site-packages/django/forms/forms.py", line 175, in errors

self.full_clean()

File "...python3.5/site-packages/django/forms/forms.py", line 386, in full_clean

self._post_clean()

File "...python3.5/site-packages/django/forms/models.py", line 408, in _post_clean

self.instance.full_clean(exclude=exclude, validate_unique=False)

File "...python3.5/site-packages/django/db/models/base.py", line 1234, in full_clean

self.clean()

File "...python3.5/site-packages/django/contrib/auth/base_user.py", line 77, in clean

setattr(self, self.USERNAME_FIELD, self.normalize_username(self.get_username()))

File "...python3.5/site-packages/django/db/models/fields/related_descriptors.py", line 216, in set

self.field.remote_field.model._meta.object_name,

ValueError: Cannot assign "'unpriv@…'": "Account.localemail" must be a "Mailbox" instance.
[21/Aug/2017 16:08:37] "POST /admin/erdb/account/19/change/ HTTP/1.1" 500 166385

Discussion:
​https://www.mail-archive.com/django-users@googlegroups.com/msg178769.html