id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
22445	Doc on reversible data migrations needed	Karen Tracey	Tim Graham	"If I create a data migration, run it, then try to migrate back to before it, I get:

{{{
  Unapplying m3app.0003_auto_20140415_1022...Traceback (most recent call last):
  File ""./manage.py"", line 10, in <module>
    execute_from_command_line(sys.argv)
  File ""/home/kmtracey/.virtualenvs/uncfm/lib/python3.3/site-packages/django/core/management/__init__.py"", line 427, in execute_from_command_line
    utility.execute()
  File ""/home/kmtracey/.virtualenvs/uncfm/lib/python3.3/site-packages/django/core/management/__init__.py"", line 419, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File ""/home/kmtracey/.virtualenvs/uncfm/lib/python3.3/site-packages/django/core/management/base.py"", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File ""/home/kmtracey/.virtualenvs/uncfm/lib/python3.3/site-packages/django/core/management/base.py"", line 337, in execute
    output = self.handle(*args, **options)
  File ""/home/kmtracey/.virtualenvs/uncfm/lib/python3.3/site-packages/django/core/management/commands/migrate.py"", line 145, in handle
    executor.migrate(targets, plan, fake=options.get(""fake"", False))
  File ""/home/kmtracey/.virtualenvs/uncfm/lib/python3.3/site-packages/django/db/migrations/executor.py"", line 62, in migrate
    self.unapply_migration(migration, fake=fake)
  File ""/home/kmtracey/.virtualenvs/uncfm/lib/python3.3/site-packages/django/db/migrations/executor.py"", line 114, in unapply_migration
    migration.unapply(project_state, schema_editor)
  File ""/home/kmtracey/.virtualenvs/uncfm/lib/python3.3/site-packages/django/db/migrations/migration.py"", line 121, in unapply
    raise Migration.IrreversibleError(""Operation %s in %s is not reversible"" % (operation, self))
django.db.migrations.migration.IrreversibleError: Operation <RunPython <function load_initial_data at 0x7f7af2424050>> in m3app.0003_auto_20140415_1022 is not reversible
}}}

I cannot find any documentation on how to create a reversible data migration. I'm used to doing this with South, I assume there is some way to do this in the new migrations framework? We need some doc on how to do it...or if this is not just a missing doc issue then this needs to be re-classified as a migrations code issue..."	Bug	closed	Documentation	1.7-beta-1	Release blocker	fixed			Accepted	0	0	0	0	0	0