id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
29283	Difference between 'apps.get_model' and 'import' in migration	bronvic	nobody	"HTR:

I have a model `UserProfile` which looks like this:
{{{
class UserProfile(VStandardModel):
    user = models.OneToOneField(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, null=True, default=None)
    mail = models.TextField(null=True, default=None, unique=True)
}}}

And I want to make migration which will do two things:
1. Change user field to `user = models.OneToOneField(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, null=False)`
2. If user was `None` set a user with an email

So I wrote a migration:
{{{
from __future__ import unicode_literals

from django.conf import settings
from django.db import migrations, models
from django.core.exceptions import ObjectDoesNotExist
from django.contrib.auth import get_user_model

import django.db.models.deletion


def empty_users(apps, schema_editor):
    UserProfile = apps.get_model('main', 'UserProfile')
    model_user = get_user_model()

    for profile in UserProfile.objects.all().only('user', 'mail'):
        if profile.user is None:
            try:
                profile.user = model_user.objects.get(email=profile.mail)
            except model_user.DoesNotExist:
                try:
                    profile.user = model_user.objects.create(email=profile.mail, is_active=False)
                except Exception as err:
                    print(err)

            profile.save()


class Migration(migrations.Migration):

    dependencies = [
        ('main', '0066_auto_20180222_1954'),
    ]

    operations = [
        migrations.RunPython(empty_users, reverse_code=migrations.RunPython.noop),
        migrations.AlterField(
            model_name='userprofile',
            name='user',
            field=models.OneToOneField(on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL),
        ),
    ]
}}}

And, as you see, I emphasized an error in `except Exception as err:`. It is: `Cannot assign ""<User: >"": ""UserProfile.user"" must be a ""User"" instance.`.

But if I change `UserProfile = apps.get_model('main', 'UserProfile')` to `from main.models import UserProfile` migration will pass. "	Bug	closed	Database layer (models, ORM)	1.11	Normal	invalid			Unreviewed	0	0	0	0	0	0