Django abstract model + DB migrations: tests throw "cannot ALTER TABLE because it has pending trigger events"

Question

I want to write an abstract model mixin, that I can use to make OneToOne - relations to the user model. Here is my code:

from django.conf import settings
from django.db import models


class Userable(models.Model):
    user = models.OneToOneField(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE
    )

    class Meta:
        abstract = True

I've written the following test for this model:

class TestUserable(TestCase):

    mixin = Userable

    def setUp(self):
        user = User.objects.create_user(
            email="[email protected]",
            name="Test User",
            password="test1234test"
        )
        self.user = user
        self.model = ModelBase(
            '__TestModel__' + self.mixin.__name__, (self.mixin,),
            {'__module__': self.mixin.__module__}
        )

        with connection.schema_editor() as schema_editor:
            schema_editor.create_model(self.model)

    def test_user(self):
        self.model.objects.create(user=self.user)
        self.assertEqual(self.model.objects.count(), 1)

    def tearDown(self):
        with connection.schema_editor() as schema_editor:
            schema_editor.delete_model(self.model)

My problem is, that this test in it's tearDown() method throws the follwing error:

django.db.utils.OperationalError: cannot DROP TABLE "core___testmodel__userable" because it has pending trigger events

What could be the cause of this? I did run python manage.py makemigrations and python manage.py migrate, but there are no pending migrations (as is expected, since this is an abstract model).

EDIT: It seems to have something to do with OneToOneFields or ForeignKeys (relations). If I use this code altered for regular fields, like CharFields or IntegerFields, it works.

EDIT2: If you have another better way of testing abstract base model that use ForeignKeys, please let me know!

Answer 1

Common practice for testing abstract models is to create actual models just for tests

here is example in model-utils project https://github.com/jazzband/django-model-utils/blob/master/tests/test_models/test_timestamped_model.py

from tests.models import UserableTest

class TestUserable(TestCase):
    def setUp(self):
        user = User.objects.create_user(
            email="[email protected]",
            name="Test User",
            password="test1234test"
        )
        self.user = user

    def test_user(self):
        UserableTest.objects.create(user=self.user)
        self.assertEqual(UserableTest.objects.count(), 1)

In this project they have separate settings DJANGO_SETTINGS_MODULE = tests.settings https://github.com/jazzband/django-model-utils/blob/master/tests/settings.py

INSTALLED_APPS = (
    'model_utils',
    'tests',
)
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3'
    }
}
SECRET_KEY = 'dummy'

And models are described in https://github.com/jazzband/django-model-utils/blob/master/tests/models.py

from myapp.models import Userable

class UserableTest(Userable):
    pass