课程3-4运行的时候报这个错误
RuntimeError: Model class message.models.UserMessage doesn’t declare an explicit app_label and isn’t in an application in INSTALLED_APPS.

setting.py里我配置’message’了

Exception in thread django-main-thread:

Traceback (most recent call last):

  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/threading.py", line 954, in _bootstrap_inner

    self.run()

  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/threading.py", line 892, in run

    self._target(*self._args, **self._kwargs)

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/utils/autoreload.py", line 64, in wrapper

    fn(*args, **kwargs)

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/core/management/commands/runserver.py", line 118, in inner_run

    self.check(display_num_errors=True)

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/core/management/base.py", line 419, in check

    all_issues = checks.run_checks(

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/core/checks/registry.py", line 76, in run_checks

    new_errors = check(app_configs=app_configs, databases=databases)

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/core/checks/urls.py", line 13, in check_url_config

    return check_resolver(resolver)

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/core/checks/urls.py", line 23, in check_resolver

    return check_method()

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/urls/resolvers.py", line 412, in check

    for pattern in self.url_patterns:

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/utils/functional.py", line 48, in __get__

    res = instance.__dict__[self.name] = self.func(instance)

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/urls/resolvers.py", line 598, in url_patterns

    patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/utils/functional.py", line 48, in __get__

    res = instance.__dict__[self.name] = self.func(instance)

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/urls/resolvers.py", line 591, in urlconf_module

    return import_module(self.urlconf_name)

  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/importlib/__init__.py", line 127, in import_module

    return _bootstrap._gcd_import(name[level:], package, level)

  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import

  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load

  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked

  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked

  File "<frozen importlib._bootstrap_external>", line 790, in exec_module

  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/djangostart/urls.py", line 18, in <module>

    from message.views import getform

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/apps/message/views.py", line 6, in <module>

    from .models import UserMessage

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/apps/message/models.py", line 9, in <module>

    class UserMessage(models.Model):

  File "/Users/jiaochen/PycharmProjects/pythonProject/djangostart/venv/lib/python3.9/site-packages/django/db/models/base.py", line 113, in __new__

    raise RuntimeError(

RuntimeError: Model class message.models.UserMessage doesn't declare an explicit app_label and isn't in an application in INSTALLED_APPS.