MySQL misbehaves when a forwards() data migration doesn't work out

[dpmcgee@…]

If the forwards() migration blows up for some reason, you get a bunch of stuff telling you that your migration wasn't marked no-dry-run, rather than seeing the actual reason the migration failed.

In this case, we have a very isolated test case set up that will always fail (trying to NULL out a non-null column), but it behaves correctly on SQLite and tells you what you are doing wrong, whereas in MySQL you get the below misleading error.

I've attached a sample app that can fully reproduce this case. There is an SQLite DB included as well to see that it in fact works fine (e.g. fails correctly) with that database engine.

Here are the steps necessary to reproduce (a mix of SQL and shell commands):

create database southbug;
create user southbug identified by 'southbug';
grant all on southbug.* to southbug;

./manage.py syncdb
./manage.py miggrate bug 0001

use southbug;
insert into bug_bug values ('testing 1', 1);
insert into bug_bug values ('testing 2', 2);
insert into bug_bug values ('testing 3', 3);

Then do the following:

$ ./manage.py migrate bug
Running migrations for bug:

• Migrating forwards to 0002_values_to_null.

  bug:0002_values_to_null
  

• Migration 'bug:0002_values_to_null' is marked for no-dry-run.

Traceback (most recent call last):

File "./manage.py", line 11, in <module>

execute_manager(settings)

File "/usr/lib/python2.6/site-packages/django/core/management/init.py", line 362, in execute_manager

utility.execute()

File "/usr/lib/python2.6/site-packages/django/core/management/init.py", line 303, in execute

self.fetch_command(subcommand).run_from_argv(self.argv)

File "/usr/lib/python2.6/site-packages/django/core/management/base.py", line 195, in run_from_argv

self.execute(*args, options.dict)

File "/usr/lib/python2.6/site-packages/django/core/management/base.py", line 222, in execute

output = self.handle(*args, options)

File "/usr/lib/python2.6/site-packages/south/management/commands/migrate.py", line 102, in handle

delete_ghosts = delete_ghosts,

File "/usr/lib/python2.6/site-packages/south/migration/init.py", line 202, in migrate_app

success = migrator.migrate_many(target, workplan, database)

File "/usr/lib/python2.6/site-packages/south/migration/migrators.py", line 215, in migrate_many

result = migrator.class.migrate_many(migrator, target, migrations, database)

File "/usr/lib/python2.6/site-packages/south/migration/migrators.py", line 284, in migrate_many

result = self.migrate(migration, database)

File "/usr/lib/python2.6/site-packages/south/migration/migrators.py", line 121, in migrate

result = self.run(migration)

File "/usr/lib/python2.6/site-packages/south/migration/migrators.py", line 95, in run

return self.run_migration(migration)

File "/usr/lib/python2.6/site-packages/south/migration/migrators.py", line 82, in run_migration

print self.run_migration_error(migration)

File "/usr/lib/python2.6/site-packages/south/migration/migrators.py", line 278, in run_migration_error

(self.format_backwards(migration), extra_info))

File "/usr/lib/python2.6/site-packages/south/migration/migrators.py", line 265, in format_backwards

self.backwards(migration)()

File "/usr/lib/python2.6/site-packages/south/migration/migrators.py", line 56, in <lambda>

return (lambda: direction(orm))

File "/tmp/southbug/bug/migrations/0002_values_to_null.py", line 15, in backwards

orm.Bug.objects.all().update(fieldname='testing ' + models.F('id'))

File "/usr/lib/python2.6/site-packages/south/orm.py", line 396, in getattr

raise AttributeError?("You are in a dry run, and cannot access the ORM.\nWrap ORM sections in 'if not db.dry_run:', or if the whole migration is only a data migration, set no_dry_run = True on the Migration class.")

AttributeError?: You are in a dry run, and cannot access the ORM.
Wrap ORM sections in 'if not db.dry_run:', or if the whole migration is only a data migration, set no_dry_run = True on the Migration class.

[dpmcgee@…]

Example app to reproduce

[andrew]

Now fixed in [9f0aac73bdf9].