Django - multiselectfiled is not working?

Question

I used Python version 3.11.3 Django version 4.2.3

And I tested multiselectfield in simple project.

models.py

from django.db import models
from multiselectfield import MultiSelectField


class Book(models.Model):
    BOOK_CHOICES = (
        ('at','at'),
        ('at2','at2'),
        ('at3','at3'),
        ('at4','at4')
    )
    title=MultiSelectField(choices=BOOK_CHOICES)

admin.py

from django.contrib import admin
from .models import Book

admin.site.register(Book)

settings.py

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'data',
    'multiselectfield',
]

Error

  File "C:\Users\Meliksah Can\Desktop\book\manage.py", line 22, in <module>
    main()
  File "C:\Users\Meliksah Can\Desktop\book\manage.py", line 18, in main
    execute_from_command_line(sys.argv)
  File "C:\Users\Meliksah Can\Desktop\book\venv\Lib\site-packages\django\core\management\__init__.py", line 442, in execute_from_command_line
    utility.execute()
  File "C:\Users\Meliksah Can\Desktop\book\venv\Lib\site-packages\django\core\management\__init__.py", line 416, in execute
    django.setup()
  File "C:\Users\Meliksah Can\Desktop\book\venv\Lib\site-packages\django\__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "C:\Users\Meliksah Can\Desktop\book\venv\Lib\site-packages\django\apps\registry.py", line 116, in populate
    app_config.import_models()
  File "C:\Users\Meliksah Can\Desktop\book\venv\Lib\site-packages\django\apps\config.py", line 269, in import_models
    self.models_module = import_module(models_module_name)
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Meliksah Can\AppData\Local\Programs\Python\Python311\Lib\importlib\__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 1204, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1176, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1147, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 690, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 940, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "C:\Users\Meliksah Can\Desktop\book\data\models.py", line 5, in <module>
    class Book(models.Model):
  File "C:\Users\Meliksah Can\Desktop\book\data\models.py", line 12, in Book
    title=MultiSelectField(choices=BOOK_CHOICES)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Meliksah Can\Desktop\book\venv\Lib\site-packages\multiselectfield\db\fields.py", line 72, in __init__
    self.validators[0] = MaxValueMultiFieldValidator(self.max_length)
    ~~~~~~~~~~~~~~~^^^
IndexError: list assignment index out of range

I want to make more than one selection in the Django Admin panel, but I could not skip this part. I will use this feature to add that a book belongs to more than one genre when saving it to the database.

Thank you in advance if anyone has had a similar problem or has any suggestions.

Answer 1

Edit your model like this:

from django.db import models
from multiselectfield import MultiSelectField

class Book(models.Model):
    BOOK_CHOICES = (
        ('at', 'at'),
        ('at2', 'at2'),
        ('at3', 'at3'),
        ('at4', 'at4')
    )
    title = MultiSelectField(choices=BOOK_CHOICES)

remove models. before MultiSelectField because it is not in the models of Django, it is a new package.

Answer 2

It's looks to be an error from the library... source code

This is a quick test to reproduce the behaviour:

>>> hello = []
>>> hello[0] = 'world'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list assignment index out of range
>>> hello = []
>>> hello.append('world')
>>> hello[0] = 'world !'

From django CharField source you can see an if statement:

if attribute max_length is into the argument an validator will be added (django source)

So to solve it, try to add max_length into MultiSelectField like:

MultiSelectField(choices=BOOK_CHOICES, max_length=2048)

But this is an issue into the library you should notice them.