Migration Woes: TypeError: int() argument must be a string... on ForeignKeys

I’m trying to alter my foreign keys on my audit log models to allow for null.  Django creates a new migration file, with an operation something like below:

 

        migrations.AlterField(

            model_name='checklistauditlogentry',

            name='usage',

            field=models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, related_name='_auditlog_checklistusages', to='general.DisplayName'),

        )

 

Upon applying the migrations, I get this error (without full path shown):

TypeError: int() argument must be a string, a bytes-like object or a number, not 'DisplayName'

 

I just can’t seem to figure this one out.  I can’t just delete the migrations and start over because I really need Django to modify the database to remove the requirement on those fields.

 

Full trace:

Running migrations:

  Applying documents.0002_auto_20170912_1445...Traceback (most recent call last):

  File "manage.py", line 10, in <module>

    execute_from_command_line(sys.argv)

  File "\lib\site-packages\django\core\management\__init__.py", line 364, in execute_from_command_line

    utility.execute()

  File "\lib\site-packages\django\core\management\__init__.py", line 356, in execute

    self.fetch_command(subcommand).run_from_argv(self.argv)

  File "\lib\site-packages\django\core\management\base.py", line 283, in run_from_argv

    self.execute(*args, **cmd_options)

  File "\lib\site-packages\django\core\management\base.py", line 330, in execute

    output = self.handle(*args, **options)

  File "\lib\site-packages\django\core\management\commands\migrate.py", line 204, in handle

    fake_initial=fake_initial,

  File "\lib\site-packages\django\db\migrations\executor.py", line 115, in migrate

    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)

  File "\lib\site-packages\django\db\migrations\executor.py", line 145, in _migrate_all_forwards

    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)

  File "\lib\site-packages\django\db\migrations\executor.py", line 244, in apply_migration

    state = migration.apply(state, schema_editor)

  File "\lib\site-packages\django\db\migrations\migration.py", line 129, in apply

    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)

  File "\lib\site-packages\django\db\migrations\operations\fields.py", line 216, in database_forwards

    schema_editor.alter_field(from_model, from_field, to_field)

  File "\lib\site-packages\django\db\backends\base\schema.py", line 515, in alter_field

    old_db_params, new_db_params, strict)

  File "\lib\site-packages\django\db\backends\postgresql\schema.py", line 112, in _alter_field

    new_db_params, strict,

  File "\lib\site-packages\django\db\backends\base\schema.py", line 612, in _alter_field

    old_default = self.effective_default(old_field)

  File "\lib\site-packages\django\db\backends\base\schema.py", line 229, in effective_default

    default = field.get_db_prep_save(default, self.connection)

  File "\lib\site-packages\django\db\models\fields\related.py", line 963, in get_db_prep_save

    return self.target_field.get_db_prep_save(value, connection=connection)

  File "\lib\site-packages\django\db\models\fields\__init__.py", line 770, in get_db_prep_save

    prepared=False)

  File "\lib\site-packages\django\db\models\fields\__init__.py", line 958, in get_db_prep_value

    value = self.get_prep_value(value)

  File "\lib\site-packages\django\db\models\fields\__init__.py", line 966, in get_prep_value

    return int(value)

TypeError: int() argument must be a string, a bytes-like object or a number, not 'DisplayName'