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
29177	Unmanaged models with ForeignKeys do not get those fields serialized into their migration state when CreateModel happens.	Keryn Knight	Michal Mládek	"Given models like the following, where `B` is unmanaged, and `C` is a normal concrete `Model`:

{{{
from django.db import models

class A(models.Model):
    class Meta:
        db_table = ""test_a""


class B(models.Model):
    a = models.ForeignKey(A, related_name=""+"", on_delete=models.CASCADE)

    class Meta:
        managed = False
        db_table = ""test_b""


class C(models.Model):
    a = models.ForeignKey(A, related_name=""+"", on_delete=models.CASCADE)

    class Meta:
    db_table = ""test_c""
}}}

when `python manage.py makemigrations <appname>` is called, `B` ends up looking like:
{{{
migrations.CreateModel(
    name='B',
    fields=[
        ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
    ],
    options={
        'db_table': 'test_b',
        'managed': False,
    },
)
}}}
whilst `C` correctly gets:
{{{
migrations.CreateModel(
    name='C',
    fields=[
        ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
        ('a', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='+', to='whee.A')),
    ],
    options={
        'db_table': 'test_c',
    },
)
}}}
Because `B` doesn't have the `a` attribute, any subsequent data migrations which would like to query on it, like so:
{{{
def forwards(apps, schema_editor):
    B = apps.get_model('whee', 'B')
    B.objects.filter(a=1)
}}}
will crash.

With the assistance of Markus on IRC:
{{{
MarkusH: do you want to try what's gonna happen when you just drop the if-condition in https://github.com/django/django/blob/75527c0f8360ae3555fcf67ce19b4cb910b69b9d/django/db/migrations/autodetector.py#L570-L572 ?
}}}

commenting out the lines
{{{
if not model_opts.managed:
    continue
}}}

allows the autodetector to generate the following:
{{{
migrations.CreateModel(
    name='B',
    fields=[
        ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
    ],
    options={
        'db_table': 'test_b',
        'managed': False,
    },
),
migrations.AddField(
    model_name='b',
    name='a',
    field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='+', to='whee.A'),
)
}}}
and subsequently the data migration can access `B.a`

If `A` itself is `managed=False` the migration generated is instead:
{{{
migrations.CreateModel(
    name='B',
    fields=[
        ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
        ('a', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='+', to='whee.A')),
    ],
    options={
        'db_table': 'test_b',
        'managed': False,
    },
)
}}}

Running the test suite via `./runtests.py` as of commit 75527c0f8360ae3555fcf67ce19b4cb910b69b9d doesn't seem to cause any failures, with those lines commented out.

Markus also pointed out commit https://github.com/django/django/commit/215aa4f53b6bbd07d5c1eecfa94e7fcd00da813e which references #23415

I noticed this ""issue"" while bringing a project up from 1.9, so it's not a recent problem.
"	Bug	assigned	Migrations	dev	Normal			Keryn Knight Daniel Naab	Accepted	1	0	0	0	0	0