#29177: Unmanaged models with ForeignKeys do not get those fields serialized
into
their migration state when CreateModel happens.
----------------------------------------+------------------------
Reporter: Keryn Knight | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
----------------------------------------+------------------------
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='A',
fields=[
('id', models.AutoField(auto_created=True, primary_key=True,
serialize=False, verbose_name='ID')),
],
options={
'db_table': 'test_a',
},
),
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.
--
Ticket URL: <https://code.djangoproject.com/ticket/29177>
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