id summary reporter owner description type status component version severity resolution keywords cc stage has_patch needs_docs needs_tests needs_better_patch easy ui_ux 28972 `RelatedObjectDoesNotExist` during `loaddata` of models with multi-table inheritance Kal Sze nobody "Software versions * Python 3.6.3 * Django 2.0 * django-model-utils 3.1.1 (from git) * PostgreSQL 9.4 * psycopg2 2.7.3.2 I have a `licenses` app, with these models: * `BaseLicense`, a concrete model, with a `ForeignKey` to `settings.AUTH_USER_MODEL`. * `CorelDrawLicense`, which inherits from `BaseLicense` through multi-table inheritance * `AdobePhotoshopLicense`, which inherits from `BaseLicense` through multi-table inheritance I created an instance of `AdobePhotoshopLicense`, then tried to do `manage.py dumpdata` and `manage.py loaddata`. `dumpdata` ""worked"" - there was no error. However, `loaddata` failed with this traceback: {{{ Traceback (most recent call last): File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/core/serializers/json.py"", line 69, in Deserializer yield from PythonDeserializer(objects, **options) File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/core/serializers/python.py"", line 170, in Deserializer obj = base.build_instance(Model, data, using) File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/core/serializers/base.py"", line 225, in build_instance natural_key = obj.natural_key() File ""/home/kal/git/nk_test/licenses/models.py"", line 33, in natural_key return (self.user.natural_key(), self.license_key) File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py"", line 175, in __get__ ""%s has no %s."" % (self.field.model.__name__, self.field.name) django.db.models.fields.related_descriptors.RelatedObjectDoesNotExist: BaseLicense has no user. The above exception was the direct cause of the following exception: Traceback (most recent call last): File ""./manage.py"", line 15, in execute_from_command_line(sys.argv) File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/core/management/__init__.py"", line 371, in execute_from_command_line utility.execute() File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/core/management/__init__.py"", line 365, in execute self.fetch_command(subcommand).run_from_argv(self.argv) File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/core/management/base.py"", line 288, in run_from_argv self.execute(*args, **cmd_options) File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/core/management/base.py"", line 335, in execute output = self.handle(*args, **options) File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/core/management/commands/loaddata.py"", line 72, in handle self.loaddata(fixture_labels) File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/core/management/commands/loaddata.py"", line 113, in loaddata self.load_label(fixture_label) File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/core/management/commands/loaddata.py"", line 168, in load_label for obj in objects: File ""/home/kal/.virtualenvs/nk_test-5iWsqJVv/lib/python3.6/site-packages/django/core/serializers/json.py"", line 73, in Deserializer raise DeserializationError() from exc django.core.serializers.base.DeserializationError: Problem installing fixture '/home/kal/git/nk_test/./fixtures/dumpdata.json': }}} Here are the exact steps: 1. Create model instances in management shell {{{ >>> from django.contrib.auth import get_user_model >>> User = get_user_model() >>> kal = User.objects.create_user('kal', 'kal@foobar.com', 'qwer1234') >>> from licenses.models import AdobePhotoshopLicense >>> l = AdobePhotoshopLicense.objects.create(user=kal, license_key='12345') }}} 2. Dump the data into a fixtures json {{{ $ python manage.py dumpdata -o fixtures.json --format json --natural-foreign --natural-primary auth licenses }}} 3. Edit settings.py to switch to an empty database {{{ DATABASES = { 'default': { 'ENGINE': 'django.db.backends.postgresql', #'NAME': 'nk_test', 'NAME': 'nk_test_2', 'USER': 'kal', 'HOST': '', 'PORT': 5432, } } }}} 4. Run migrations on the new empty database {{{ $ python manage.py migrate }}} 5. Try to load the data from fixtures.json {{{ $ python manage.py loaddata --format json fixtures.json }}} I have attached the `models.py` and `fixtures.json` files to the ticket. I know that I don't (and I can't) enforce the natural key uniqueness at the database level. However, due to my application logic, I know that the user+license_key combination is effectively unique for any one of the child license models. And this is specifically allowed, [https://docs.djangoproject.com/en/2.0/topics/serialization/#deserialization-of-natural-keys according to the documentation]: [U]niqueness doesn’t need to be enforced at the database level. If you are certain that a set of fields will be effectively unique, you can still use those fields as a natural key. Also note that this bug doesn't have to do with my use of the custom `InheritanceManager`. I could let the `BaseLicense` model use the default manager and still get the same bug." Bug closed Core (Serialization) 2.0 Normal duplicate Unreviewed 0 0 0 0 0 0