django.db.utils.IntegrityError: FOREIGN KEY constraint failed while executing LiveServerTestCases through Selenium and Python Django

Question

I can run all unit tests successfully, I can even run selenium tests successfully if I run an independent server, but when I try to use LiveServerTestCases to test everything in a self-contained manner, each LiveServerTestCase test ends with the following error after completing the tearDown function:

  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\db\backends\base\base.py", line 239, in _commit
    return self.connection.commit()
django.db.utils.IntegrityError: FOREIGN KEY constraint failed

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\test\testcases.py", line 209, in __call__
    self._post_teardown()
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\test\testcases.py", line 908, in _post_teardown
    self._fixture_teardown()
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\test\testcases.py", line 943, in _fixture_teardown
    inhibit_post_migrate=inhibit_post_migrate)
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\core\management\__init__.py", line 148, in call_command
    return command.execute(*args, **defaults)
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\core\management\base.py", line 353, in execute
    output = self.handle(*args, **options)
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\core\management\commands\flush.py", line 80, in handle
    emit_post_migrate_signal(verbosity, interactive, database)
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\core\management\sql.py", line 51, in emit_post_migrate_signal
    **kwargs
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\dispatch\dispatcher.py", line 175, in send
    for receiver in self._live_receivers(sender)
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\dispatch\dispatcher.py", line 175, in <listcomp>
    for receiver in self._live_receivers(sender)
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\contrib\auth\management\__init__.py", line 79, in create_permissions
    Permission.objects.using(using).bulk_create(perms)
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\db\models\query.py", line 471, in bulk_create
    obj_without_pk._state.db = self.db
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\db\transaction.py", line 212, in __exit__
    connection.commit()
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\db\backends\base\base.py", line 261, in commit
    self._commit()
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\db\backends\base\base.py", line 239, in _commit
    return self.connection.commit()
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\db\utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\db\backends\base\base.py", line 239, in _commit
    return self.connection.commit()
django.db.utils.IntegrityError: FOREIGN KEY constraint failed

I'm pretty sure I don't have any errors in my database models, as all the unit tests run fine and the selenium tests run fine when I fire up a seperate server instance to run in parallel, so I'm guessing it has to do with selenium?

I've tried using the Chrome webdriver, IE webdriver and Firefox webdriver. Same results. It doesn't appear to be related to my database as the error only occurs for LiveServerTestCases.

Environment Details

• Django version 2.1
• SQLite3 version 3.20.0

Answer 1

Some more information regarding the Django version, Database type and version along with your code trials would have helped us to debug this issue in a better way.

However, this error message...

File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\core\management\sql.py", line 51, in emit_post_migrate_signal **kwargs
.
File "C:\Users\Win7\.virtualenvs\lang-QbOXb8q_\lib\site-packages\django\db\backends\base\base.py", line 239, in _commit
    return self.connection.commit()
django.db.utils.IntegrityError: FOREIGN KEY constraint failed

...implies that an IntegrityError was raised while attempting to save an existing model instance.

As per Django 2.0 release notes:

• Foreign key constraints are now enabled on SQLite: This was a backwards-incompatible change (IntegrityError: FOREIGN KEY constraint failed) if attempting to save an existing model instance that’s violating a foreign key constraint.

• Foreign Keys are now created with DEFERRABLE INITIALLY DEFERRED instead of DEFERRABLE IMMEDIATE. So the tables may need to be rebuilt to recreate foreign keys with the new definition, particularly if you’re using a pattern as follows;

  from django.db import transaction
  
  with transaction.atomic():
      Book.objects.create(author_id=1)
      Author.objects.create(id=1)
  

• If you don’t recreate the foreign key as DEFERRED, the first create() would fail as the foreign key constraints are enforced.

• @dirkgroten in this discussion provided an example as follows:

  • Look for patterns like this in your code:

     # in pagetree/models.py, line 810
     @classmethod
     def create_from_dict(cls, d):
        return cls.objects.create()  # what happens to d by the way?
    

  • This will definitely fail with a ForeignKey constraint error since a PageBlock must have section, so you can't call create without first assigning it.