[1.8.x] Fixed #24287 -- Added friendly error if a model is in a models.py outside an installed app.

import copy

import inspect

from itertools import chain

import sys

import warnings

from itertools import chain

from django.apps import apps

from django.apps.config import MODELS_MODULE_NAME

from django.conf import settings

from django.core import checks

from django.core.exceptions import (FieldDoesNotExist, ObjectDoesNotExist,

    MultipleObjectsReturned, FieldError, ValidationError, NON_FIELD_ERRORS)

from django.db import (router, connections, transaction, DatabaseError,

    DEFAULT_DB_ALIAS, DJANGO_VERSION_PICKLE_KEY)

from django.core.exceptions import (

    NON_FIELD_ERRORS, FieldDoesNotExist, FieldError, ImproperlyConfigured,

    MultipleObjectsReturned, ObjectDoesNotExist, ValidationError,

)

from django.db import (

    DEFAULT_DB_ALIAS, DJANGO_VERSION_PICKLE_KEY, DatabaseError, connections,

    router, transaction,

)

from django.db.models import signals

from django.db.models.constants import LOOKUP_SEP

from django.db.models.deletion import Collector

from django.db.models.fields import AutoField

from django.db.models.fields.related import (ForeignObjectRel, ManyToOneRel,

    OneToOneField, add_lazy_relation)

from django.db.models.fields.related import (

    ForeignObjectRel, ManyToOneRel, OneToOneField, add_lazy_relation,

)

from django.db.models.manager import ensure_default_manager

from django.db.models.options import Options

from django.db.models.query import Q

from django.db.models.query_utils import DeferredAttribute, deferred_class_factory

from django.db.models.query_utils import (

    DeferredAttribute, deferred_class_factory,

)

from django.utils import six

from django.utils.deprecation import RemovedInDjango19Warning

from django.utils.encoding import force_str, force_text

from django.utils.functional import curry

from django.utils.six.moves import zip

from django.utils.text import get_text_list, capfirst

from django.utils.text import capfirst, get_text_list

from django.utils.translation import ugettext_lazy as _

from django.utils.version import get_version

                    app_label_index = package_components.index(MODELS_MODULE_NAME) + 1

                except ValueError:

                    app_label_index = 1

                try:

                    kwargs = {"app_label": package_components[app_label_index]}

                except IndexError:

                    raise ImproperlyConfigured(

                        'Unable to detect the app label for model "%s." '

                        'Ensure that its module, "%s", is located inside an installed '

                        'app.' % (new_class.__name__, model_module.__name__)

                    )

            else:

                kwargs = {"app_label": app_config.label}

from __future__ import unicode_literals

import os

import sys

from django.apps import apps

from django.core.exceptions import ImproperlyConfigured

from django.db import models

from django.test import TestCase

from django.test.utils import extend_sys_path

from django.utils._os import upath

        self.assertNotIn(

            "NotInstalledModel",

            [m.__name__ for m in apps.get_models()])

    def test_exception_raised_if_model_declared_outside_app(self):

        class FakeModule(models.Model):

            __name__ = str("models_that_do_not_live_in_an_app")

        sys.modules['models_not_in_app'] = FakeModule

        def declare_model_outside_app():

            models.base.ModelBase.__new__(

                models.base.ModelBase,

                str('Outsider'),

                (models.Model,),

                {'__module__': 'models_not_in_app'})

        msg = (

            'Unable to detect the app label for model "Outsider." '

            'Ensure that its module, "models_that_do_not_live_in_an_app", '

            'is located inside an installed app.'

        )

        with self.assertRaisesMessage(ImproperlyConfigured, msg):

            declare_model_outside_app()