[Django]-How to add a new record with a guest (anonymous) user in Django

So, if I understand correctly, you can do this a few ways:

1. The easiest way is to simply set the login_user field nullable and blank or,
2. Create a "guest user" and "guest author" in your Django database that is not active (is_active is set to False so they can’t log in) and all anonymous users are assigned that User and Author instance the database.

As mentioned, the simplest method would be just to set the login_user field as nullable and blank, like such:

login_user = models.ForeignKey(Author, on_delete=models.CASCADE, blank=True, null=True)

And if your get_author() returns None, then simply leave that column blank, though this might affect other parts of your application if an Author or User object is required elsewhere.

Another way to do it in your get_author() method using a "guest" user:

def get_author(user):
    if user.is_anonymous:
        guest_user = User.objects.get(username="guest") # or whatever ID or name you use for the placeholder user that no one will be assigned
        guest_author = Author.objects.get_or_create(user=guest_user)
        return guest_author
     else:
        return Author.objects.get(user=user) 

In this option, you’d need to set your department field in Author to blank and null or set a default like:

class Author(models.Model):
      user = ...
      department = ...(..., default="none")

or

 class Author(models.Model):
       user = ...
       department = ...(..., blank=True, null=True)

Yet another option might be to create a new "guest" user for each action:

import random
import string

def randomString(stringLength):
    letters = string.ascii_letters
    return ''.join(random.choice(letters) for i in range(stringLength))

def get_author(user):
        if user.is_anonymous:
            random_username = f"{randomString(10)}_guest"
            random_email = f"{randomString(5)}_guest@example.com"
            guest_user = User.objects.create(username=random_username, is_active=False, email=random_email...) 
            guest_author = Author.objects.create(user=guest_user, department="none")
            return guest_author
         else:
            return Author.objects.get(user=user)

Thank you for your help and time. I chose the second solution after little change.

def get_author(user):
    if user.is_anonymous:
        guest_user = User.objects.get(username="guest") # or whatever ID or name you use for the placeholder user that no one will be assigned
        qs = Author.objects.filter(user=guest_user)
        if qs.exists():
            return qs[0]
        return None
     else:
        qs = Author.objects.filter(user=user)
        if qs.exists():
            return qs[0]
        return None

Now is little better and working well.
When I use exactly your method was little mistake: "ValueError: Cannot assign "(<Author: guest>, False)": "hardware.login_user" must be a "Author" instance."

So, anyway thank you again.