Postgresql – TypeError: ForeignKey(None) is invalid. First parameter to ForeignKey must be either a model, a model name, or the string 'self'

I recently developed a web app and tested its deployment on Nginx and it worked just fine. The client has a preference for Apache though and I created a config file. After this, I am getting a 500 server error and the error above is presenting itself.

Below is part of the traceback in the Apache error log:

[Tue Aug 06 19:48:10.945075 2024] [wsgi:error] [pid 344644] [remote 169.255.52.63:23675]   File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
[Tue Aug 06 19:48:10.945077 2024] [wsgi:error] [pid 344644] [remote 169.255.52.63:23675]   File "<frozen importlib._bootstrap_external>", line 883, in exec_module
[Tue Aug 06 19:48:10.945079 2024] [wsgi:error] [pid 344644] [remote 169.255.52.63:23675]   File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
[Tue Aug 06 19:48:10.945082 2024] [wsgi:error] [pid 344644] [remote 169.255.52.63:23675]   File "/var/www/mysite/vir/lib/python3.10/site-packages/django/contrib/admin/models.py", line 48, in <module>
[Tue Aug 06 19:48:10.945086 2024] [wsgi:error] [pid 344644] [remote 169.255.52.63:23675]     class LogEntry(models.Model):
[Tue Aug 06 19:48:10.945089 2024] [wsgi:error] [pid 344644] [remote 169.255.52.63:23675]   File "/var/www/mysite/vir/lib/python3.10/site-packages/django/contrib/admin/models.py", line 54, in LogEntry
[Tue Aug 06 19:48:10.945090 2024] [wsgi:error] [pid 344644] [remote 169.255.52.63:23675]     user = models.ForeignKey(
[Tue Aug 06 19:48:10.945092 2024] [wsgi:error] [pid 344644] [remote 169.255.52.63:23675]   File "/var/www/mysite/vir/lib/python3.10/site-packages/django/db/models/fields/related.py", line 959, in __init__
[Tue Aug 06 19:48:10.945094 2024] [wsgi:error] [pid 344644] [remote 169.255.52.63:23675]     raise TypeError(
[Tue Aug 06 19:48:10.945099 2024] [wsgi:error] [pid 344644] [remote 169.255.52.63:23675] TypeError: ForeignKey(None) is invalid. First parameter to ForeignKey must be either a model, a model name, or the string 'self'

I opened django/db/models/fields/related.py and found the source of the exception:

def __init__(
        self,
        to,
        on_delete,
        related_name=None,
        related_query_name=None,
        limit_choices_to=None,
        parent_link=False,
        to_field=None,
        db_constraint=True,
        **kwargs,
    ):
        try:
            to._meta.model_name
        except AttributeError:
            if not isinstance(to, str):
                raise TypeError(
                    "%s(%r) is invalid. First parameter to ForeignKey must be "
                    "either a model, a model name, or the string %r"
                    % (
                        self.__class__.__name__,
                        to,
                        RECURSIVE_RELATIONSHIP_CONSTANT,
                    )
                )

I know this definitely has to do with failure to establish a connection to the Postgres db but what is exactly causing this?

• I have tried changing the db host to that of the server. I get a socket error
• I have also changed the psql socket group ownership to www-data but the 500 server error persists.

Running ./manage.py dbshell is working just fine.

Here is my Apache config file:

<VirtualHost *:80>
        # The ServerName directive sets the request scheme, hostname and port that
        # the server uses to identify itself. This is used when creating
        # redirection URLs. In the context of virtual hosts, the ServerName
        # specifies what hostname must appear in the request's Host: header to
        # match this virtual host. For the default virtual host (this file) this
        # value is not decisive as it is used as a last resort host regardless.
        # However, you must set it for any further virtual host explicitly.
        #ServerName www.example.com
        ServerAdmin [email protected]
        DocumentRoot /var/www/mysite
        ServerName mysite.com
    Alias /static /var/www/mysite/portal/static

    <Directory /var/www/mysite/portal/static>
        Require all granted
    </Directory>
    Alias /media /home/admin/media
    <Directory /home/admin/media>
                Require all granted
        </Directory>
    <Directory /var/www/mysite/portal/portal>
        <Files wsgi.py>
            Require all granted
        </Files>
    </Directory>
    WSGIDaemonProcess portal python-path=/var/www/mysite/portal python-home=/var/www/mysite/vir
    WSGIProcessGroup portal
    WSGIScriptAlias / /var/www/mysite/portal/portal/wsgi.py
    ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

and this is the wsgi.py file:

import os

from django.core.wsgi import get_wsgi_application

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'portal.settings')

application = get_wsgi_application()

Any insight would be greatly appreciated. Thanks!

EDIT

I’ve edited to add part of my settings.py file:

WSGI_APPLICATION = 'portal.wsgi.application'


# Database
# https://docs.djangoproject.com/en/5.0/ref/settings/#databases

DATABASES = {
   'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': os.getenv('DB_NAME'),
        'USER': os.getenv('DB_USER'),
        'PASSWORD': os.getenv('DB_PASSWORD'),
        'HOST': os.getenv('DB_HOST'),
        'PORT': ''
   }
}

# User authentication

AUTH_USER_MODEL = os.getenv("AUTH_USER_MODEL")
AUTHENTICATION_BACKENDS = ['login.backends.EmailBackend',]

where DB_HOST = 127.0.0.1 and the server is on 41.XX.XX.XX, AUTH_USER_MODEL = 'login.CustomUser'

and directory tree:

.
├── portal
│   ├── login
│   ├── manage.py
│   ├── portal
│   ├── static
│   ├── templates
│   └── web
├── README.md
├── requirements.txt
└── vir
    ├── bin
    ├── include
    ├── lib
    ├── lib64 -> lib
    └── pyvenv.cfg