Django migrate model with user in a foreignkey fails - django

Question

Im trying to migrate my django model:
from django.contrib.auth.models import User
class Post(models.Model):
headline = models.CharField(max_length=200)
slug = models.SlugField(max_length=200)
body = models.TextField(blank=True, null=True)
author = models.ForeignKey(User, null=True, blank=True)
I added the author field after I created the model.
Here is the migration django creates:
# encoding: utf8
from django.db import models, migrations
class Migration(migrations.Migration):
dependencies = [('articles', '0002_auto')]
operations = [
migrations.AddField(
field = models.ForeignKey(to_field=u'id', to=u'auth.User', blank=True, null=True),
name = 'author',
model_name = 'post',
),
]
Here is my traceback when I try to run ./manage.py migrate:
Operations to perform:
Synchronize unmigrated apps: ckeditor, sessions, admin, messages, auth, staticfiles, contenttypes, django_extensions
Apply all migrations: articles
Synchronizing apps without migrations:
Creating tables...
Installing custom SQL...
Installing indexes...
Installed 0 object(s) from 0 fixture(s)
Running migrations:
Applying articles.0002_post_author...Traceback (most recent call last):
File "./manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/core/management/__init__.py", line 397, in execute_from_command_line
utility.execute()
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/core/management/__init__.py", line 390, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/core/management/base.py", line 242, in run_from_argv
self.execute(*args, **options.__dict__)
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/core/management/base.py", line 289, in execute
output = self.handle(*args, **options)
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/core/management/commands/migrate.py", line 116, in handle
executor.migrate(targets, plan, fake=options.get("fake", False))
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/migrations/executor.py", line 60, in migrate
self.apply_migration(migration, fake=fake)
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/migrations/executor.py", line 73, in apply_migration
migration.apply(project_state, schema_editor)
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/migrations/migration.py", line 80, in apply
operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/migrations/operations/fields.py", line 22, in database_forwards
schema_editor.add_field(from_model, to_model._meta.get_field_by_name(self.name)[0])
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/backends/schema.py", line 349, in add_field
definition, params = self.column_sql(model, field, include_default=True)
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/backends/schema.py", line 105, in column_sql
db_params = field.db_parameters(connection=self.connection)
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/models/fields/related.py", line 1285, in db_parameters
return {"type": self.db_type(connection), "check": []}
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/models/fields/related.py", line 1276, in db_type
rel_field = self.related_field
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/models/fields/related.py", line 1183, in related_field
return self.foreign_related_fields[0]
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/models/fields/related.py", line 971, in foreign_related_fields
return tuple(rhs_field for lhs_field, rhs_field in self.related_fields)
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/models/fields/related.py", line 958, in related_fields
self._related_fields = self.resolve_related_fields()
File "/home/USER/.virtualenvs/PROJECT/src/django-trunk/django/db/models/fields/related.py", line 943, in resolve_related_fields
raise ValueError('Related model %r cannot been resolved' % self.rel.to)
ValueError: Related model u'auth.User' cannot been resolved
Anyone know what I'm doing wrong?

Answer 1

What helped me in this situation:
Delete all migration files except __init__.py (/%prjname%/migrations folder)
python manage.py makemigrations
python manage.py migrate
Not sure about exact cause, but i tried to use files, generated by my code-partner and it didn't work out.

Answer 2

Ok, this is another funky feature of Django which cost me hours to figure it out. According to https://docs.djangoproject.com/en/1.8/topics/auth/customizing/#substituting-a-custom-user-model:
Due to limitations of Django’s dynamic dependency feature for swappable models, you must ensure that the model referenced by AUTH_USER_MODEL is created in the first migration of its app (usually called 0001_initial); otherwise, you will have dependency issues.
So to solve this problem the best "clean" way is to put your custom user model creation in 0001_initial.py and it will simply work. And that's the real reason why Lebedev Sergey's delete/makemigrations trick can work.

Answer 3

If you make this change after you have applied ANY other migrations, you need to delete everything else in the migration folder and then run "python manage.py makemigrations". Then whatever you used for AUTH_USER_MODEL will be your first migration.

Answer 4

This probably isn't your problem if you're not using a custom user model, but remember to always use get_user_model() or when referencing the User class. Also, when defining a foreign key, settings.AUTH_USER_MODEL works, too, as in:
class MyModel(models.Model):
person = models.ForeignKey(settings.AUTH_USER_MODEL)