Django-cms with custom user model: LookupError: Model 'accounts.CustomUser' not registered

Using Django 3.2/Django-cms 3.11.

I am encountering an issue when trying to add PlaceholderField from cms.models.fields in my events.models module to the EventVenue model.

from cms.models.fields import PlaceholderField
class EventVenue(models.Model):
    name = models.CharField(_('name'), max_length=255)
    slider = PlaceholderField('room_slider')

the settings:

INSTALLED_APPS = [
    'modeltranslation',
    'djangocms_admin_style',
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'django.contrib.sites',
    'django.forms',
    
    'haystack',
    'accounts',
    'cms',
    'menus',
    'treebeard',
    'sekizai',
    'filer',
    'easy_thumbnails',
    'mptt',
    'simple_history',
    'crispy_forms',
    'crispy_bootstrap5',

    'djangocms_text_ckeditor',
    'djangocms_link',
    'djangocms_file',
    'djangocms_picture',
    'djangocms_video',
    'djangocms_googlemap',
    'djangocms_snippet',
    'djangocms_style',
    'djangocms_forms',
    'django_flatpickr',
    'phonenumber_field',

    'bgv_cms',
    'ddz_cms',
    'events',
    'mail_list',
]
AUTH_USER_MODEL = 'accounts.CustomUser'

the custom user class:

class CustomUser(AbstractUser):
    organization = models.ForeignKey(Organization, on_delete=models.SET_NULL,blank=True, null=True, related_name='employee')
    mailing_list = models.ManyToManyField(to='MailList', related_name='mail_list', blank=True, verbose_name=_('Mailing lists'))
    room = models.CharField(_('Room Mailing Lists'), max_length=100, choices=FLOOR, blank=True, null=True)
    email = models.EmailField(_('email address'), unique=True)

    USERNAME_FIELD = 'email'
    REQUIRED_FIELDS = ('username',)

    objects = CustomUserManager()

    def __str__(self):
        return self.get_full_name() or self.username

Here's the relevant part of the traceback:

from events.models import EventVenue
  File "C:\Users\SAIF\Desktop\projects\bgv\bgv\events\models.py", line 17, in <module>
    from cms.models.fields import PlaceholderField
  File "C:\Users\SAIF\Anaconda3\envs\bgv\lib\site-packages\cms\models\__init__.py", line 3, in <module>
    from .permissionmodels import *  # nopyflakes
  File "C:\Users\SAIF\Anaconda3\envs\bgv\lib\site-packages\cms\models\permissionmodels.py", line 19, in <module>
    User = apps.get_registered_model(user_app_name, user_model_name)
  File "C:\Users\SAIF\Anaconda3\envs\bgv\lib\site-packages\django\apps\registry.py", line 273, in get_registered_model
    raise LookupError(
LookupError: Model 'accounts.CustomUser' not registered.

i have tried to change the app order in the INSTALLED_APPS and inherit from the PermissionsMixin in the custom user but didn't work

the Organization class in the accounts app:

class Organization(models.Model):
    name = models.CharField(max_length=255)
    contact_person = models.ForeignKey(settings.AUTH_USER_MODEL, 
                                       on_delete=models.CASCADE,
                                       blank=True, null=True, 
                                       help_text=_('if you changed the contact person to another user, you lose access to this organization info.'),
                                       related_name='owner')
responsible_for_room = models.ForeignKey(EventVenue, on_delete=models.SET_NULL,blank=True, null=True, related_name='responsible_for_room')
    def __str__(self):
        return self.name

After a few tests with adding AUTH_USER_MODEL in my current project, my conclusions are the following:

• using AUTH_USER_MODEL with the django-cms requires attention to detail
• changing INSTALLED_APPS orders could help, but not for me (and not the OP)
• what helped for me, was making sure, that my app that contains the AUTH_USER_MODEL imports nothing at all cms related (i.e. no PageField, no models, no helpers or anything. Can't list all of it, but you'll get it). Because this will trigger loading of the permissionsmodel, which wants to import the user model. Also, any app (in INSTALLED_APPS) before the one containing your user should consequently not import anything cms.

So for this specific case/question, it would mean checking the accounts app for any cms imports. And also, for any other imports that could trigger cms imports, as for example the Organization - this could be removed, and the foreign key be noted as models.ForeignKey("organization_app.Organization",....) - as I don't know where Organization lives.

This is not fully researched, but could help anyway. Fun fact: If you specify AUTH_USER_MODEL = "auth.User" everything runs ok.