Unable to load initial data with ForeignKey field during migration in 1.7b4

[make.kernel@…]

Here is a models.py from my really simple demoapp

from django.db import models

class SimpleModel(models.Model):
    pass

class ModelWithReference(models.Model):
    simplemodel = models.ForeignKey(SimpleModel, related_name='modelswithreference')

And migrations

in file 0001_initial.py

# encoding: utf8
from __future__ import unicode_literals

from django.db import models, migrations

class Migration(migrations.Migration):

    dependencies = [
    ]

    def load_initial_data(apps, schema_editor):
        simplemodel = apps.get_model('demoapp', 'SimpleModel')
        simplemodel.objects.create(id=1)
        simplemodel.objects.create(id=2)

    operations = [
        migrations.CreateModel(
            name='SimpleModel',
            fields=[
                ('id', models.AutoField(serialize=False, auto_created=True, verbose_name='ID', primary_key=True)),
            ],
            options={
            },
            bases=(models.Model,),
        ),
        migrations.RunPython(load_initial_data)
    ]

and file 0002_modelwithreference.py


# encoding: utf8
from __future__ import unicode_literals

from django.db import models, migrations

class Migration(migrations.Migration):

    dependencies = [
        ('demoapp', '0001_initial'),
    ]

    def load_initial_data(apps, shema_editor):
        simplemodel = apps.get_model('demoapp', 'SimpleModel').objects.get(pk=1)
        modelwithreference = apps.get_model('demoapp', 'ModelWithReference')

        modelwithreference.objects.create(id=1, simplemodel=simplemodel)

    operations = [
        migrations.CreateModel(
            name='ModelWithReference',
            fields=[
                ('id', models.AutoField(serialize=False, primary_key=True, verbose_name='ID', auto_created=True)),
                ('simplemodel', models.ForeignKey(to='demoapp.SimpleModel', to_field='id')),
            ],
            options={
            },
            bases=(models.Model,),
        ),
        migrations.RunPython(load_initial_data)
    ]

Exception is

Running migrations:
  Applying demoapp.0001_initial... OK
  Applying demoapp.0002_modelwithreference...Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/core/management/__init__.py", line 427, in execute_from_command_line
    utility.execute()
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/core/management/__init__.py", line 419, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/core/management/base.py", line 337, in execute
    output = self.handle(*args, **options)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/core/management/commands/migrate.py", line 146, in handle
    executor.migrate(targets, plan, fake=options.get("fake", False))
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/migrations/executor.py", line 62, in migrate
    self.apply_migration(migration, fake=fake)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/migrations/executor.py", line 96, in apply_migration
    migration.apply(project_state, schema_editor)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/migrations/migration.py", line 107, in apply
    operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/migrations/operations/special.py", line 117, in database_forwards
    self.code(from_state.render(), schema_editor)
  File "/home/yuriy/dev/python/projects/demo/demoapp/migrations/0002_modelwithreference.py", line 16, in load_initial_data
    modelwithreference.objects.create(id=1, simplemodel=simplemodel)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/models/manager.py", line 92, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/models/query.py", line 368, in create
    obj = self.model(**kwargs)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/models/base.py", line 444, in __init__
    setattr(self, field.name, rel_obj)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/models/fields/related.py", line 597, in __set__
    self.field.rel.to._meta.object_name,
ValueError: Cannot assign "<SimpleModel: SimpleModel object>": "ModelWithReference.simplemodel" must be a "SimpleModel" instance.

Somehow it works if I get initial data loading from 0002_modelwithreference.py to another file, for example

file 0003_loadinitialdata.py

# encoding: utf8
from __future__ import unicode_literals

from django.db import models, migrations


class Migration(migrations.Migration):

    dependencies = [
        ('demoapp', '0002_modelwithreference'),
    ]

    def load_initial_data(apps, shema_editor):
        simplemodel = apps.get_model('demoapp', 'SimpleModel').objects.get(pk=1)
        modelwithreference= apps.get_model('demoapp', 'ModelWithReference')

        modelwithreference.objects.create(id=1, simplemodel=simplemodel)

    operations = [
        migrations.RunPython(load_initial_data),
    ]

but it raises exception on first run and works on second. Result is:

(rest) yuriy@yuriy-$ rm db.sqlite3 
(rest) yuriy@yuriy-$ ./manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: sessions, admin, auth, contenttypes
  Apply all migrations: demoapp
Synchronizing apps without migrations:
  Creating tables...
    Creating table django_admin_log
    Creating table auth_permission
    Creating table auth_group_permissions
    Creating table auth_group
    Creating table auth_user_groups
    Creating table auth_user_user_permissions
    Creating table auth_user
    Creating table django_content_type
    Creating table django_session
  Installing custom SQL...
  Installing indexes...
Running migrations:
  Applying demoapp.0001_initial... OK
  Applying demoapp.0002_modelwithreference... OK
  Applying demoapp.0003_loadinitialdata...Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/core/management/__init__.py", line 427, in execute_from_command_line
    utility.execute()
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/core/management/__init__.py", line 419, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/core/management/base.py", line 337, in execute
    output = self.handle(*args, **options)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/core/management/commands/migrate.py", line 146, in handle
    executor.migrate(targets, plan, fake=options.get("fake", False))
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/migrations/executor.py", line 62, in migrate
    self.apply_migration(migration, fake=fake)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/migrations/executor.py", line 96, in apply_migration
    migration.apply(project_state, schema_editor)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/migrations/migration.py", line 107, in apply
    operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/migrations/operations/special.py", line 117, in database_forwards
    self.code(from_state.render(), schema_editor)
  File "/home/yuriy/dev/python/projects/demo/demoapp/migrations/0003_loadinitialdata.py", line 17, in load_initial_data
    modelwithreference.objects.create(id=1, simplemodel=simplemodel)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/models/manager.py", line 92, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/models/query.py", line 368, in create
    obj = self.model(**kwargs)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/models/base.py", line 444, in __init__
    setattr(self, field.name, rel_obj)
  File "/home/yuriy/dev/python/environments/rest/lib/python3.4/site-packages/django/db/models/fields/related.py", line 597, in __set__
    self.field.rel.to._meta.object_name,
ValueError: Cannot assign "<SimpleModel: SimpleModel object>": "ModelWithReference.simplemodel" must be a "SimpleModel" instance.
(rest) yuriy@yuriy-$ ./manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: contenttypes, sessions, admin, auth
  Apply all migrations: demoapp
Synchronizing apps without migrations:
  Creating tables...
  Installing custom SQL...
  Installing indexes...
Running migrations:
  Applying demoapp.0003_loadinitialdata... OK

You have installed Django's auth system, and don't have any superusers defined.
Would you like to create one now? (yes/no): no
(rest) yuriy@yuriy-$ 

Note, that I removed database: rm db.sqlite3
first run ./manage.py migrate - exception, second run ./manage.py migrate - Applying demoapp.0003_loadinitialdata... OK

[make.kernel@…]

source code of demoapp application and migrations

[Simon Charette]

Could you try to see if the patch proposed in #22659 solves your issue.

I think both are related since CreateModel operation are special cased and might reuse model state fields which could be the source of the ValueError you're encountering.

[make.kernel@…]

Yes, it solves issues, with this patch migrations work as expected.

Thanks a lot for fast answer and solution.

[Simon Charette]

Alright I'll mark this ticket as duplicate of #22659 in this case.