#25293: Multi-table inheritance with only related fields results in invalid
migration on MySQL
----------------------------+--------------------
Reporter: hbielenia | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 1.8
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
----------------------------+--------------------
This report may be a duplicate of
https://code.djangoproject.com/ticket/24424 , but since the scope is
somewhat different and proposed fix would not solve the issue, I decided
to report it separately.
On Django 1.8.2, I have following model:
{{{
class Client(User):
mailing_list = models.OneToOneField(SubscriberList, null=True,
default=None)
}}}
Using manage.py makemigrations generates following operations:
{{{
operations = [
migrations.CreateModel(
name='Client',
fields=[
('id', models.AutoField(verbose_name='ID',
serialize=False, auto_created=True, primary_key=True)),
('user',
models.OneToOneField(to=settings.AUTH_USER_MODEL)),
],
),
migrations.RemoveField(
model_name='client',
name='id',
),
migrations.RemoveField(
model_name='client',
name='user',
),
migrations.AddField(
model_name='client',
name='mailing_list',
field=models.OneToOneField(null=True, default=None,
to='campaign.SubscriberList'),
),
migrations.AddField(
model_name='client',
name='user_ptr',
field=models.OneToOneField(parent_link=True,
auto_created=True, primary_key=True, default=0, serialize=False,
to=settings.AUTH_USER_MODEL),
preserve_default=False,
),
]
}}}
As you can see, the migration starts by removing implicit `id` and `user`
fields, to later substitute them with implicit `user_ptr` field that
serves both as foreign and primary key. Unfortunately,
`migrations.RemoveField` uses `ALTER TABLE` statements, and this code
attempts to delete all columns on the table, resulting in OperationalError
with MySQL 5.8:
`_mysql_exceptions.OperationalError: (1090, "You can't delete all columns
with ALTER TABLE; use DROP TABLE instead")`.
It looks to me like an unwanted behaviour.
--
Ticket URL: <https://code.djangoproject.com/ticket/25293>
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