#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 | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
----------------------------+------------------------------------
Changes (by timgraham):
* stage: Unreviewed => Accepted
Old description:
> 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:
> `django.db.utils.OperationalError: (1090, "You can't delete all columns
> with ALTER TABLE; use DROP TABLE instead")`.
>
> It looks to me like an unwanted behaviour.
New description:
This report may be a duplicate of #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:
`django.db.utils.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#comment:2>
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