https://github.com/zacharyvoase/django-migrationbug-poc
A proof-of-concept for a bug in Django v1.8 migrations
https://github.com/zacharyvoase/django-migrationbug-poc
Last synced: 2 months ago
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A proof-of-concept for a bug in Django v1.8 migrations
- Host: GitHub
- URL: https://github.com/zacharyvoase/django-migrationbug-poc
- Owner: zacharyvoase
- Created: 2016-01-14T21:35:56.000Z (over 9 years ago)
- Default Branch: master
- Last Pushed: 2016-01-14T21:38:13.000Z (over 9 years ago)
- Last Synced: 2025-06-14T17:55:42.928Z (4 months ago)
- Language: Python
- Size: 4.88 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Django 1.8 Migration Bug Proof-of-Concept
I've identified a bug in migrations in Django 1.8 w/ Postgres (that definitely
wasn't present in v1.7).
## Bug Description
If you have a field like:
name = models.CharField(..., db_index=True)
And you add a unique constraint without removing the `db_index=True`:
name = models.CharField(..., db_index=True, unique=True)
The auto-migration you get from that looks like:
migrations.AlterField(
model_name='person',
name='name',
field=models.CharField(db_index=True, unique=True, max_length=255, blank=True),
)
When Django tries to run this migration you get:
```
Operations to perform:
Synchronize unmigrated apps: staticfiles, messages
Apply all migrations: admin, contenttypes, migration_poc_app, auth, sessions
Synchronizing apps without migrations:
Creating tables...
Running deferred SQL...
Installing custom SQL...
Running migrations:
Rendering model states... DONE
Applying contenttypes.0001_initial... OK
Applying auth.0001_initial... OK
Applying admin.0001_initial... OK
Applying contenttypes.0002_remove_content_type_name... OK
Applying auth.0002_alter_permission_name_max_length... OK
Applying auth.0003_alter_user_email_max_length... OK
Applying auth.0004_alter_user_username_opts... OK
Applying auth.0005_alter_user_last_login_null... OK
Applying auth.0006_require_contenttypes_0002... OK
Applying migration_poc_app.0001_initial... OK
Applying migration_poc_app.0002_auto_20160114_2114...Traceback (most recent call last):
File "manage.py", line 10, in
execute_from_command_line(sys.argv)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/core/management/__init__.py", line 354, in execute_from_command_line
utility.execute()
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/core/management/__init__.py", line 346, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/core/management/base.py", line 394, in run_from_argv
self.execute(*args, **cmd_options)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/core/management/base.py", line 445, in execute
output = self.handle(*args, **options)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 222, in handle
executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/db/migrations/executor.py", line 110, in migrate
self.apply_migration(states[migration], migration, fake=fake, fake_initial=fake_initial)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/db/migrations/executor.py", line 148, in apply_migration
state = migration.apply(state, schema_editor)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/db/migrations/migration.py", line 115, in apply
operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/db/migrations/operations/fields.py", line 201, in database_forwards
schema_editor.alter_field(from_model, from_field, to_field)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 484, in alter_field
old_db_params, new_db_params, strict)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/db/backends/postgresql_psycopg2/schema.py", line 113, in _alter_field
self.execute(like_index_statement)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 111, in execute
cursor.execute(sql, params)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/db/backends/utils.py", line 79, in execute
return super(CursorDebugWrapper, self).execute(sql, params)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/db/utils.py", line 98, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
File "/Users/zack/src/migration_poc/venv/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: relation "migration_poc_app_person_name_32437daa2f5b1fe9_like" already exists
```
**N.B.:** If you remove the `db_index=True` from the `AlterField(...)` call,
the migration succeeds, even if the field definition in the model still has
`db_index=True`.
## Repro Instructions
This repo includes a minimal Django project that produces the error.
1. Create a virtualenv and install Django and psycopg2:
```
virtualenv venv
. venv/bin/activate
pip install -r requirements.txt
```
2. Install Postgres, e.g. from [Postgres.app](http://postgresapp.com)
3. Edit `migration_poc/settings.py` to point to your local Postgres instance
4. Create a `migration_poc` database:
```
createdb migration_poc
```
5. Run the migration:
```
python manage.py migrate
```
This should produce the error.
You can make changes to the auto-migration and models.py, then just run `dropdb
migration_poc; createdb migration_poc` to reset the DB and try migrating again.
This is how I found out that removing the `db_index=True` param from
`AlterField` side-steps the issue.