django.db.utils.OperationalError: 1005, 'Can't create table `xyz`.`#sql-600_237` (errno: 150 "Foreign key constraint is incorrectly formed")

Question

I am trying to add One-to-One keys into my Django app, but I always get that error when I try to "migrate" process (makemigrations works great).

  Applying xyzapp.0007_personne_extended_foreign...Traceback (most recent call last):
  File "manage.py", line 29, in <module>
    execute_from_command_line(sys.argv)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 354, in execute_from_command_line
utility.execute()
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 346, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/core/management/base.py", line 394, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/core/management/base.py", line 445, in execute
    output = self.handle(*args, **options)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 222, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 110, in migrate
    self.apply_migration(states[migration], migration, fake=fake, fake_initial=fake_initial)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 148, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 91, in __exit__
    self.execute(sql)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 111, in execute
    cursor.execute(sql, params)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 79, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/db/utils.py", line 98, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "/opt/xyz/env/local/lib/python2.7/site-packages/django/db/backends/mysql/base.py", line 124, in execute
    return self.cursor.execute(query, args)
  File "/usr/lib/python2.7/dist-packages/MySQLdb/cursors.py", line 226, in execute
    self.errorhandler(self, exc, value)
  File "/usr/lib/python2.7/dist-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
    raise errorvalue
django.db.utils.OperationalError: (1005, 'Can\'t create table `xyz`.`#sql-600_297` (errno: 150 "Foreign key constraint is incorrectly formed")')

That's what my models looks like :

class PersonVolunteer(models.Model):
    person = models.OneToOneField(Person)

class Person(models.Model):
    name = models.CharField(max_length=100)

And the migration process that cause the crash :

class Migration(migrations.Migration):

dependencies = [
    ('xyzapp', '0014_member_to_person'),
]

operations = [
    migrations.CreateModel(
        name='PersonVolunteer',
        fields=[
            ('id', models.AutoField(verbose_name='ID', serialize=False, auto_created=True, primary_key=True)),
            ('personne', models.OneToOneField(to='xyzapp.Personne')),
        ],
    ),
]

However, all works correctly when I test it even after the migrate error. But if that error message appears during "migrate", that should not be something good happening. If there's no problem, it is possible to skip that last step which crash my migration ?

Can someone can say me why do I get that error message and how I can resolve it ?

Thank you very much and have a great day !

Answer 1

I have found a solution, may be not the cleaner, but god dammit it works, that's perfect for me.

# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import migrations, models

class Migration(migrations.Migration):

    dependencies = [
        ('cvmapp', '0006_person_extended'),
    ]

    operations = [
        migrations.AddField(
            model_name='PersonVolunteer',
            name='personne',
            field=models.OneToOneField(related_name='info_volunteer', to='cvmapp.Person', db_constraint=False),
        ),
    ]

The trick was to add "db_constraint=False" as a parameter of the OneToOne field.