LookupError: No installed app with label 'admin'. What is the problem?

Question

Django

Colleagues, good afternoon.
Googled, but due to inexperience, did not find a solution to the problem.
I just started learning python, got to the chapter with django.
Added the first "Topic" model, the migration was successful. But after adding a new Entry model, and trying to migrate, it gives an error:

Traceback (most recent call last):
  File "manage.py", line 21, in <module>
    main()
  File "manage.py", line 17, in main
    execute_from_command_line(sys.argv)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\core\management\__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\core\management\__init__.py", line 357, in execute
    django.setup()
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\apps\registry.py", line 114, in populate
    app_config.import_models()
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\apps\config.py", line 211, in import_models
    self.models_module = import_module(models_module_name)
  File "C:\Users\Nooqi\AppData\Local\Programs\Python\Python37\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "D:\!python\learning_log\learning_logs\models.py", line 13, in <module>
    class Entry(models.Model):
  File "D:\!python\learning_log\learning_logs\models.py", line 15, in Entry
    topic = models.ForeignKey(Topic)
TypeError: __init__() missing 1 required positional argument: 'on_delete'

Then I decided to reboot the virtual environment:

Watching for file changes with StatReloader
Exception in thread Thread-1:
Traceback (most recent call last):
  File "C:\Users\Nooqi\AppData\Local\Programs\Python\Python37\lib\threading.py", line 917, in _bootstrap_inner
    self.run()
  File "C:\Users\Nooqi\AppData\Local\Programs\Python\Python37\lib\threading.py", line 865, in run
    self._target(*self._args, **self._kwargs)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\utils\autoreload.py", line 54, in wrapper
    fn(*args, **kwargs)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\core\management\commands\runserver.py", line 109, in inner_run
    autoreload.raise_last_exception()
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\utils\autoreload.py", line 77, in raise_last_exception
    raise _exception[0](_exception[1]).with_traceback(_exception[2])
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\utils\autoreload.py", line 54, in wrapper
    fn(*args, **kwargs)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\apps\registry.py", line 114, in populate
    app_config.import_models()
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\apps\config.py", line 211, in import_models
    self.models_module = import_module(models_module_name)
  File "C:\Users\Nooqi\AppData\Local\Programs\Python\Python37\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "D:\!python\learning_log\learning_logs\models.py", line 13, in <module>
    class Entry(models.Model):
  File "D:\!python\learning_log\learning_logs\models.py", line 15, in Entry
    topic = models.ForeignKey(Topic)
TypeError: __init__() missing 1 required positional argument: 'on_delete'

Traceback (most recent call last):
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\apps\registry.py", line 155, in get_app_config
    return self.app_configs[app_label]
KeyError: 'admin'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "manage.py", line 21, in <module>
    main()
  File "manage.py", line 17, in main
    execute_from_command_line(sys.argv)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\core\management\__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\core\management\__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\core\management\base.py", line 323, in run_from_argv
    self.execute(*args, **cmd_options)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\core\management\commands\runserver.py", line 60, in execute
    super().execute(*args, **options)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\core\management\base.py", line 364, in execute
    output = self.handle(*args, **options)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\core\management\commands\runserver.py", line 95, in handle
    self.run(**options)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\core\management\commands\runserver.py", line 102, in run
    autoreload.run_with_reloader(self.inner_run, **options)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\utils\autoreload.py", line 579, in run_with_reloader
    start_django(reloader, main_func, *args, **kwargs)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\utils\autoreload.py", line 564, in start_django
    reloader.run(django_main_thread)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\utils\autoreload.py", line 272, in run
    get_resolver().urlconf_module
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\utils\functional.py", line 80, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\urls\resolvers.py", line 564, in urlconf_module
    return import_module(self.urlconf_name)
  File "C:\Users\Nooqi\AppData\Local\Programs\Python\Python37\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "D:\!python\learning_log\learning_log\urls.py", line 20, in <module>
    path('admin/', admin.site.urls),
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\utils\functional.py", line 256, in inner
    self._setup()
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\contrib\admin\sites.py", line 529, in _setup
    AdminSiteClass = import_string(apps.get_app_config('admin').default_site)
  File "D:\!python\learning_log\ll-env\lib\site-packages\django\apps\registry.py", line 162, in get_app_config
    raise LookupError(message)
LookupError: No installed app with label 'admin'.

Googled, they write that the problem is with migrations from other applications, if such a model already exists somewhere. But there seems to be nothing.
code from models.py

from django.db import models

# Create your models here.

class Topic(models.Model):
    """Тема, которую изучает пользователь"""
    text = models.CharField(max_length=200)
    date_added = models.DateTimeField(auto_now_add=True)
    def __str__(self):
        """Возвращает строковое представление модели."""
        return self.text

class Entry(models.Model):
    """Информация, изученная пользователем по теме."""
    topic = models.ForeignKey(Topic)
    text = models.TextField()
    date_added = models.DateTimeField(auto_now_add=True)

    class Meta:
        verbose_name_plural = 'entries'

    def __str__(self):
        """Возращавает строковое представление модели."""
        return self.text[:50] + "..."

code from settings.py cutouts with installed applications

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    #Мои приложения
    'learning_logs'
]

If you comment out the Entry model in models.py, then everything works fine again.

Answer 1

the problem is in the file,
please post the code. it looks like the admin is not connected correctly

Answer 2

topic = models.ForeignKey(Topic)
The required parameter "on_delete=" is missing here