Migration that switches a model to a UUID primary key fails with "duplicate column name: id"

[Richard Ebeling]

We migrated a model from a AutoField as id (default behaviour) to a UUIDField in the past, using a migration that looked like this with django 2.0:
​https://gist.github.com/smcoll/8bb867dc631433c01fd0

There was a bug in SQLite though, which as of today only has the workaround listed in the bug tracker: #28541

Thus, we ended up writing our migration like this: ​https://github.com/fsr-itse/EvaP/blob/master/evap/evaluation/migrations/0062_replace_textanswer_id_with_uuid.py

When we try updating to django 2.1 now, this migration fails whenever you call migrate with the error
django.db.utils.ProgrammingError: multiple primary keys for table "evaluation_textanswer" are not allowed

This commit changed the behavior: 02365d3f38a64a5c2f3e932f23925a381d5bb151

It works if we add a RemoveField instruction for the old id before setting primary_key=True on the new UUIDField. But this will trigger the SQLite bug listed above. Changing the old AutoField to primary_key=False where the RemoveField instruction would be doesn't fix the error.

The documentation states that ​an object may not have more than one primary key.

Still, in the release notes for django 2.1 it should be noted that django's behavior was changed here. Also, I would appreciate if there was some kind of documentation on how you should migrate primary keys from a field to another if no two primary keys are allowed in between. There should be a way without squashing the migrations as we want to keep the history.

We are running postgres version 9.6.9 and psycopg2-binary version 2.7.5.
The migration error will not occur when using a SQLite database.

[Tim Graham]

It's unclear if the behavior change was intentional. Can you provide a sample project and ​bisect to find the commit where the behavior changed?

[Richard Ebeling]

This commit changed the behavior: 02365d3f38a64a5c2f3e932f23925a381d5bb151

As a sample project I can link the project we are currently working on, ​https://github.com/fsr-itse/EvaP/tree/release. A simple ./manage.py reset_db --noinput && ./manage.py migrate will trigger the error. Is this what you wanted?

[Tim Graham]

Perhaps I've made a mistake, but I tried the sample project and don't see the crash when running migrations. I tried the "master" and "release" branches and modified the DATABASES setting to use SQLite. A more minimal project to reproduce the problem would be nice.

[Richard Ebeling]

I can not reproduce this bug with SQLite either, sorry for not testing that before. We are running postgres version 9.6.9 and use psycopg2-binary version 2.7.5.. I added this information to the initial post.

[Tim Graham]

I'm attaching a minimal application that reproduces the problem (with PostgreSQL). I'm not sure that this problem should be included in the release notes rather than fixed (if possible). Solving #28541 may be more worthwhile.

[Christian Kreuzberger]

Hi!

We are also affected by this bug, see this Github issue: ​https://github.com/anx-ckreuzberger/django-rest-passwordreset/issues/8

I basically had a model that had this as primary key:

class ResetPasswordToken(models.Model):
    key = models.CharField(
        _("Key"),
        max_length=64,
        primary_key=True
    )

And I wanted to use a different primary key now:

class ResetPasswordToken(models.Model):
    id = models.AutoField(
        primary_key=True
    )

    # Key field, though it is not the primary key of the model
    key = models.CharField(
        _("Key"),
        max_length=64,
        db_index=True,
        unique=True
    )

which lead to the following migration (including some "self-written" runpython stuff to fill the primary keys):

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.conf import settings
from django.db import migrations, models
import django.db.models.deletion


def populate_auto_incrementing_pk_field(apps, schema_editor):
    ResetPasswordToken = apps.get_model('django_rest_passwordreset', 'ResetPasswordToken')

    # Generate values for the new id column
    for i, o in enumerate(ResetPasswordToken.objects.all()):
        o.id = i + 1
        o.save()


class Migration(migrations.Migration):

    dependencies = [
        ('django_rest_passwordreset', '0001_initial',),
    ]

    operations = [
        migrations.AddField(
            model_name='resetpasswordtoken',
            name='id',
            field=models.IntegerField(null=True),
            preserve_default=True,
        ),
        migrations.RunPython(
            populate_auto_incrementing_pk_field,
            migrations.RunPython.noop
        ),
        # add primary key information to id field
        migrations.AlterField(
            model_name='resetpasswordtoken',
            name='id',
            field=models.AutoField(primary_key=True, serialize=False)
        ),
        # remove primary key information from 'key' field
        migrations.AlterField(
            model_name='resetpasswordtoken',
            name='key',
            field=models.CharField(db_index=True, max_length=64, unique=True, verbose_name='Key'),
        ),
    ]

Unfortunately, this migration only works with Django 1.11 and 2.0, but not with the 2.1.1 (and also 2.1.2), where it spits out the following error:

  File "manage.py", line 31, in <module>
    execute_from_command_line(sys.argv)
  File "\venv\lib\site-packages\django\core\management\__init__.py", line 381, in execute_from_command_line

    utility.execute()
  File "\venv\lib\site-packages\django\core\management\__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "\venv\lib\site-packages\django\core\management\base.py", line 316, in run_from_argv
    self.execute(*args, **cmd_options)
  File "\venv\lib\site-packages\django\core\management\base.py", line 353, in execute
    output = self.handle(*args, **options)
  File "\venv\lib\site-packages\django\core\management\base.py", line 83, in wrapped
    res = handle_func(*args, **kwargs)
  File "\venv\lib\site-packages\django\core\management\commands\migrate.py", line 203, in handle
    fake_initial=fake_initial,
  File "\venv\lib\site-packages\django\db\migrations\executor.py", line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "\venv\lib\site-packages\django\db\migrations\executor.py", line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "\venv\lib\site-packages\django\db\migrations\executor.py", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "\venv\lib\site-packages\django\db\migrations\migration.py", line 124, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "\venv\lib\site-packages\django\db\migrations\operations\fields.py", line 216, in database_forwards
    schema_editor.alter_field(from_model, from_field, to_field)
  File "\venv\lib\site-packages\django\db\backends\base\schema.py", line 523, in alter_field
    old_db_params, new_db_params, strict)
  File "\venv\lib\site-packages\django\db\backends\postgresql\schema.py", line 122, in _alter_field
    new_db_params, strict,
  File "\venv\lib\site-packages\django\db\backends\base\schema.py", line 719, in _alter_field
    "columns": self.quote_name(new_field.column),
  File "\venv\lib\site-packages\django\db\backends\base\schema.py", line 133, in execute
    cursor.execute(sql, params)
  File "\venv\lib\site-packages\django\db\backends\utils.py", line 100, in execute
    return super().execute(sql, params)
  File "\venv\lib\site-packages\django\db\backends\utils.py", line 68, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "\venv\lib\site-packages\django\db\backends\utils.py", line 77, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "\venv\lib\site-packages\django\db\backends\utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "\venv\lib\site-packages\django\db\utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "\venv\lib\site-packages\django\db\backends\utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: Multiple primary keys for table «django_rest_passwordreset_resetpasswordtoken» are not allowed.

I thought I would be able to fix this by changing the order of creating/deleting the primary key within that migration. Now it works with Django 2.1, but not with 1.11 (and also not with 2.0), where it spits out this error:

Operations to perform:
  Apply all migrations: admin, auth, contenttypes, django_rest_passwordreset, sessions
Running migrations:
  Applying django_rest_passwordreset.0002_pk_migration...Traceback (most recent call last):
  File "/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
psycopg2.ProgrammingError: multiple primary keys for table "django_rest_passwordreset_resetpasswordtoken" are not allowed

So essentially I can not have my django package compatible with Django 2.1, as I want to maintain compatibility with the 1.11 LTS.

I also took a quick look at the example of Tim Graham, this seems to be exactly the same problem.

[Simon Charette]

If you want to maintain Django 1.11 support you could add a RunPython operation that does something along the following before the swapped AlterField

def delete_primary_key(apps, schema_editor):
    model = apps.get_model('django_rest_passwordreset', 'ResetPasswordToken')
    opts = model._meta
    connection = schema_editor.connection
    # Retrieve primary key constraint.
    with connection.cursor() as cursor:
        constraints = connection.introspection.get_constraints(cursor, opts.db_table)
    for constraint_name, constraint in constraints.items():
        if constraint.get('primary_key'):
            break
    else:
        raise Exception('Missing primary key constraint')
    # Delete primary key constraint
    quote_name = connection.ops.quote_name
    schema_editor.execute(schema_editor.sql_delete_pk.format(
        table_name=quote_name(table_name),
        name=quote_name(constraint_name),
    ))