#27339: Adding an AutoField prompts for a default which creates a broken
migration
------------------------------------------------+------------------------
Reporter: Tim Graham | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Migrations | Version: master
Severity: Normal | Keywords:
Triage Stage: Accepted | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
------------------------------------------------+------------------------
Change:
{{{
class Foo(models.Model):
id = models.CharField(max_length=20, primary_key=True)
}}}
to:
{{{
class Foo(models.Model):
character_id = models.AutoField(primary_key=True)
}}}
The created migration has these operations:
{{{
migrations.RemoveField(
model_name='foo',
name='id',
),
migrations.AddField(
model_name='foo',
name='character_id',
field=models.AutoField(default=0, primary_key=True, serialize=False),
preserve_default=False,
),
}}}
(entering 0 at the default prompt). Running the migration on PostgreSQL
gives: `ProgrammingError: multiple default values specified for column
"character_id" of table "t27267_foo"`. I'm not sure if this can be made to
work sensibly. Removing the default from the migration operation works,
but if there's an existing data, the `character_id` field must be
populated somehow (perhaps a `RunPython` could be done in the same
migration?). #27338 is related. This was discovered while investigating
#27267.
--
Ticket URL: <https://code.djangoproject.com/ticket/27339>
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