Migration Woes: TypeError: int() argument must be a string... on ForeignKeys
Matthew Pava
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'
Matthew Pava
Okay, after much investigation, I found that the default value on this exact field was actually a callable that returned an instance of DisplayName rather than the pk. After changing that, the migrations ran successfully. I wonder if Django could provide a better hint of such issues. It’s strange because that default was on the previous migration file in the AddField command, but the migrate command never threw an error. It only threw it on AlterField, and the default didn’t even have to be specified in the AlterField version.
Thank you,
Matthew
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Melvyn Sopacua
the field, so default isn't called. If you had existing data, then it
would've triggered.
What default should return for foreign keys is actually documented:
> For fields like ForeignKey that map to model instances, defaults should be the value of the field they reference (pk unless to_field is set) instead of model instances.
https://docs.djangoproject.com/en/1.11/ref/models/fields/#default
--
Melvyn Sopacua