Django External Schema Evolution Branch

This project allows you to make Django model changes without having to drop and re-add tables. This project started as a Google Summer of Code project in 2006.

Quick Start

To start using deseb, add the import deseb line after you set DJANGO_SETTINGS_MODULE in your manage.py. Like this:

#!/usr/bin/env python
import os
import sys

if __name__ == "__main__":
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "myproject.settings")
    import deseb    # <-- ADD THIS LINE
    from django.core.management import execute_from_command_line

    execute_from_command_line(sys.argv)

How it Works

Let's say I have the following model:

class Review(models.Model):
  when = models.DateTimeField(default=datetime.datetime.now)
  text = models.TextField(blank=True, null=True)
  rating = models.IntegerField(default=0)
  appt = models.ForeignKey(Appointment)
  user = models.ForeignKey(User)
  uuid = UUIDField(version=4)

And I want to add a new column response:

class Review(models.Model):
  when = models.DateTimeField(default=datetime.datetime.now)
  text = models.TextField(blank=True, null=True)
  response = models.TextField(blank=True, null=True)
  rating = models.IntegerField(default=0)
  appt = models.ForeignKey(Appointment)
  user = models.ForeignKey(User)
  uuid = UUIDField(version=4)

If I run ./manage.py evolvedb, I'll see:

$ ./manage.py evolvedb
appthub: the following schema upgrade is available:
ALTER TABLE `appthub_review` ADD COLUMN `response` longtext;
do you want to run the preceeding commands?
type 'yes' to continue, or 'no' to cancel: yes
schema upgrade executed

Now suppose I changed my mind on what that column should be called - it should be response_text:

class Review(models.Model):
  when = models.DateTimeField(default=datetime.datetime.now)
  text = models.TextField(blank=True, null=True)
  response_text = models.TextField(blank=True, null=True, aka='response')
  rating = models.IntegerField(default=0)
  appt = models.ForeignKey(Appointment)
  user = models.ForeignKey(User)
  uuid = UUIDField(version=4)

Now I run ./manage.py evolvedb again:

$ ./manage.py evolvedb
appthub: the following schema upgrade is available:
ALTER TABLE `appthub_review` CHANGE COLUMN `response` `response_text` longtext NULL;
do you want to run the preceeding commands?
type 'yes' to continue, or 'no' to cancel: yes
schema upgrade executed

Now supposed I thought this was a bad idea to begin with, so I change my model back to its original form:

class Review(models.Model):
  when = models.DateTimeField(default=datetime.datetime.now)
  text = models.TextField(blank=True, null=True)
  rating = models.IntegerField(default=0)
  appt = models.ForeignKey(Appointment)
  user = models.ForeignKey(User)
  uuid = UUIDField(version=4)

Now run ./manage.py evolvedb again:

$ ./manage.py evolvedb
appthub: the following schema upgrade is available:
-- warning: the following may cause data loss
ALTER TABLE `appthub_review` DROP COLUMN `response_text`;
-- end warning
do you want to run the preceeding commands?
type 'yes' to continue, or 'no' to cancel: yes
schema upgrade executed