Opened 11 years ago

Closed 11 years ago

Last modified 11 years ago

#22073 closed Bug (fixed)

Backwards migration on ManyToMany field does not remove intermediary table

Reported by: Ben Davis Owned by: Andrew Godwin
Component: Migrations Version: dev
Severity: Release blocker Keywords:
Cc: Ben Davis Triage Stage: Accepted
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description

When a migration is performed where a ManyToMany field is added, the intermediary table is automatically created. However, when performing a backwards migration, this table is not deleted. Consider the following:

# locations/models.py

from products.models import Product

class Location(models.Model):
    name = models.CharField(max_length=100)
    products_sold = models.ManyToManyField(Product)

We create our initial migration for locations and run it:

$ ./manage.py makemigrations locations
Migrations for 'locations':
  0001_initial.py:
      - Create model Location

$ ./manage.py migrate locations
Operations to perform:
  Apply all migrations: locations
Running migrations:
  Applying locations.0001_initial... OK

Now, if we want to, we should be able to undo that migration and re-apply it. Often in development I re-do my initial migrations to keep things simple before I do my first deployment. Unfortunately when you re-aplly the migration we get an exception, because the backward migration didn't remove the intermediary table:

$ ./manage.py migrate locations zero
Operations to perform:
  Unapply all migrations: locations
Running migrations:
  Unapplying locations.0001_initial... OK

$ ./manage.py migrate locations
Operations to perform:
  Apply all migrations: locations
Running migrations:
  Applying locations.0001_initial...Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/tmp/djangotest/src/django/django/core/management/__init__.py", line 427, in execute_from_command_line
    utility.execute()
  ...
  File "/tmp/djangotest/src/django/django/db/backends/utils.py", line 77, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/tmp/djangotest/src/django/django/db/backends/utils.py", line 61, in execute
    return self.cursor.execute(sql, params)
  File "/tmp/djangotest/src/django/django/db/utils.py", line 93, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/tmp/djangotest/src/django/django/db/backends/utils.py", line 61, in execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: relation "locations_location_products_sold" already exists

I've attached an example project where this can be reproduced.

Attachments (1)

myproject.tar.gz (2.4 KB ) - added by Ben Davis 11 years ago.
example project

Download all attachments as: .zip

Change History (9)

by Ben Davis, 11 years ago

Attachment: myproject.tar.gz added

example project

comment:1 by Ben Davis, 11 years ago

Cc: Ben Davis added

comment:2 by Ben Davis, 11 years ago

Needs tests: set

comment:3 by Ben Davis, 11 years ago

Has patch: set
Needs tests: unset

I've created a pull request with a fix and a new test for the creation of models with M2M fields: https://github.com/django/django/pull/2315

comment:4 by Tim Graham, 11 years ago

Triage Stage: UnreviewedReady for checkin

comment:5 by Markus Holtermann, 11 years ago

Triage Stage: Ready for checkinAccepted

comment:6 by Andrew Godwin, 11 years ago

Owner: set to Andrew Godwin
Status: newassigned

comment:7 by Ben Davis <bendavis78@…>, 11 years ago

Resolution: fixed
Status: assignedclosed

In df2652c44836374bb8a691e755edbc153805f9cc:

Fixed #22073 - Ensure CreateTable operation handles backwards migration correctly when M2M fields are present

comment:8 by Andrew Godwin <andrew@…>, 11 years ago

In cdf6eba1816669bd77a28da903d931b5a4b15992:

Merge pull request #2315 from bendavis78/issues/22073

Fixed #22073 - Ensure CreateTable operation handles backwards migration correctly when M2M fields are present

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