#32486: Migration which removes UniqueTogether constraint containing a
ForeignKey
fails with MariaDB (MySQL)
-----------------------------------------+------------------------
Reporter: yeputons | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 3.1
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 |
-----------------------------------------+------------------------
This issue closely resembles #24757 to me, but on a recent Django.
Note that it's MySQL-specific, I was unable to reproduce it with SQLite3
backend.
== Steps to reproduce ==
1. Create an empty project with a MySQL backend, and an app with two
models (alternatively, clone my GitHub repo from
https://github.com/yeputons/django-unique-constraint-remove-bug and skip
`makemigrations` and editing steps):
{{{
from django.db import models
class ModelA(models.Model):
pass
class ModelB(models.Model):
a_ptr = models.ForeignKey(ModelA, on_delete=models.CASCADE)
x = models.IntegerField()
class Meta:
constraints = [
models.UniqueConstraint(fields=['a_ptr', 'x'],
name='%(app_label)s_%(class)s_unique_a_ptr_x'), # (1)
]
}}}
2. Get the following migration by running `python manage.py
makemigrations`:
{{{
# Generated by Django 3.1.3 on 2021-02-27 11:59
from django.db import migrations, models
import django.db.models.deletion
class Migration(migrations.Migration):
initial = True
dependencies = [
]
operations = [
migrations.CreateModel(
name='ModelA',
fields=[
('id', models.AutoField(auto_created=True,
primary_key=True, serialize=False, verbose_name='ID')),
],
),
migrations.CreateModel(
name='ModelB',
fields=[
('id', models.AutoField(auto_created=True,
primary_key=True, serialize=False, verbose_name='ID')),
('x', models.IntegerField()),
('a_ptr',
models.ForeignKey(on_delete=django.db.models.deletion.CASCADE,
to='demo_app.modela')),
],
),
migrations.AddConstraint(
model_name='modelb',
constraint=models.UniqueConstraint(fields=('a_ptr', 'x'),
name='demo_app_modelb_unique_a_ptr_x'),
),
]
}}}
3. Successfully apply the migration by running `python manage.py migrate`
4. Then comment out the line `(1)` above and get the following migration
by `python manage.py makemigrations`:
{{{
# Generated by Django 3.1.3 on 2021-02-27 11:59
from django.db import migrations
class Migration(migrations.Migration):
dependencies = [
('demo_app', '0001_initial'),
]
operations = [
migrations.RemoveConstraint(
model_name='modelb',
name='demo_app_modelb_unique_a_ptr_x',
),
]
}}}
5. Run `python manage.py migrate`
=== Expected result ===
The migration succeeds and the result is as if there were no
`UniqueConstraint` in the first place.
=== Actual result ===
The following error gets reported:
{{{
Operations to perform:
Target specific migration: 0002_auto_20210227_1459, from demo_app
Running migrations:
Applying demo_app.0002_auto_20210227_1459...Traceback (most recent call
last):
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\db\backends\utils.py", line 84, in _execute
return self.cursor.execute(sql, params)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\mysql\connector\django\base.py", line 149, in execute
return self.cursor.execute(query, new_args)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\mysql\connector\cursor.py", line 569, in execute
self._handle_result(self._connection.cmd_query(stmt))
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\mysql\connector\connection.py", line 651, in cmd_query
result = self._handle_result(self._send_cmd(ServerCmd.QUERY, query))
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\mysql\connector\connection.py", line 538, in _handle_result
raise errors.get_exception(packet)
mysql.connector.errors.DatabaseError: 1553 (HY000): Cannot drop index
'demo_app_modelb_unique_a_ptr_x': needed in a foreign key constraint
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "manage.py", line 22, in <module>
main()
File "manage.py", line 18, in main
execute_from_command_line(sys.argv)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\core\management\__init__.py", line 401, in
execute_from_command_line
utility.execute()
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\core\management\__init__.py", line 395, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\core\management\base.py", line 330, in run_from_argv
self.execute(*args, **cmd_options)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\core\management\base.py", line 371, in execute
output = self.handle(*args, **options)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\core\management\base.py", line 85, in wrapped
res = handle_func(*args, **kwargs)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\core\management\commands\migrate.py", line 243, in handle
post_migrate_state = executor.migrate(
File "C:\Program Files (x86)\Python38-32\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 "C:\Program Files (x86)\Python38-32\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 "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\db\migrations\executor.py", line 227, in apply_migration
state = migration.apply(state, schema_editor)
File "C:\Program Files (x86)\Python38-32\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 "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\db\migrations\operations\models.py", line 843, in
database_forwards
schema_editor.remove_constraint(model, constraint)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\db\backends\base\schema.py", line 368, in
remove_constraint
self.execute(sql)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\db\backends\base\schema.py", line 142, in execute
cursor.execute(sql, params)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\db\backends\utils.py", line 98, in execute
return super().execute(sql, params)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\db\backends\utils.py", line 66, in execute
return self._execute_with_wrappers(sql, params, many=False,
executor=self._execute)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\db\backends\utils.py", line 75, in _execute_with_wrappers
return executor(sql, params, many, context)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\db\backends\utils.py", line 84, in _execute
return self.cursor.execute(sql, params)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\db\utils.py", line 90, in __exit__
raise dj_exc_value.with_traceback(traceback) from exc_value
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\django\db\backends\utils.py", line 84, in _execute
return self.cursor.execute(sql, params)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\mysql\connector\django\base.py", line 149, in execute
return self.cursor.execute(query, new_args)
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\mysql\connector\cursor.py", line 569, in execute
self._handle_result(self._connection.cmd_query(stmt))
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\mysql\connector\connection.py", line 651, in cmd_query
result = self._handle_result(self._send_cmd(ServerCmd.QUERY, query))
File "C:\Program Files (x86)\Python38-32\lib\site-
packages\mysql\connector\connection.py", line 538, in _handle_result
raise errors.get_exception(packet)
django.db.utils.DatabaseError: (1553, "1553 (HY000): Cannot drop index
'demo_app_modelb_unique_a_ptr_x': needed in a foreign key constraint",
'HY000')
}}}
=== Versions ===
* 10.4.14-MariaDB - mariadb.org binary distribution (installed by XAMPP)
* Python 3.8.0 (tags/v3.8.0:fa919fd, Oct 14 2019, 19:21:23) [MSC v.1916 32
bit (Intel)]
* django.VERSION == (3, 1, 3, 'final', 0)
* Windows 7 Pro En x64
--
Ticket URL: <https://code.djangoproject.com/ticket/32486>
Django <https://code.djangoproject.com/>
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