python - RuntimeError:モデルクラスdjango_messages.models.Messageは明示的なapp_labelを宣言しておらず、INSTALLED_APPSのアプリケーションにはありません

Question

メッセージング用にhttps://github.com/arneb/django-messagesパッケージを使用しようとしており、次のことを試しました

pip install git+https://github.com/arneb/django-messages.git

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'django.contrib.sites',
    'rest_framework',
    'rest_framework.authtoken',
    'oauth2_provider',
    'api',
    'localflavor',
    'django_localflavor_us',
    'django_countries',
    'haystack',
    'django_messages',

]

urlpatterns = [
    url(r'^admin/', admin.site.urls),
    url(r'^messages/', include('django_messages.urls')),
]

実行するpython manage.py runserverと、次のエラーが発生しました。

Unhandled exception in thread started by <function wrapper at 0x107cedaa0>
Traceback (most recent call last):
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/utils/autoreload.py", line 226, in wrapper
    fn(*args, **kwargs)
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 121, in inner_run
    self.check(display_num_errors=True)
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/core/management/base.py", line 374, in check
    include_deployment_checks=include_deployment_checks,
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/core/management/base.py", line 361, in _run_checks
    return checks.run_checks(**kwargs)
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/core/checks/registry.py", line 81, in run_checks
    new_errors = check(app_configs=app_configs)
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/core/checks/urls.py", line 14, in check_url_config
    return check_resolver(resolver)
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/core/checks/urls.py", line 24, in check_resolver
    for pattern in resolver.url_patterns:
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/utils/functional.py", line 35, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/urls/resolvers.py", line 313, in url_patterns
    patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/utils/functional.py", line 35, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/urls/resolvers.py", line 306, in urlconf_module
    return import_module(self.urlconf_name)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
  File "/Users/shivakrishna/shiva/Office_projects/iPitch/project /project /urls.py", line 23, in <module>
    url(r'^messages/', include('django_messages.urls')),
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/conf/urls/__init__.py", line 50, in include
    urlconf_module = import_module(urlconf_module)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django_messages/urls.py", line 4, in <module>
    from django_messages.views import *
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django_messages/views.py", line 11, in <module>
    from django_messages.models import Message
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django_messages/models.py", line 48, in <module>
    class Message(models.Model):
  File "/Users/shivakrishna/.virtualenvs/project /lib/python2.7/site-packages/django/db/models/base.py", line 113, in __new__
    "INSTALLED_APPS." % (module, name)
RuntimeError: Model class django_messages.models.Message doesn't declare an explicit app_label and isn't in an application in INSTALLED_APPS.

そのエラーが発生する理由とその解決方法を知ることはできますか?