Question

I’m trying to do a django-south migration to an existing application to add django-audit-log to it (to track user-initiated changes of a module), but am running into significant errors. Specifically with the action_user_id field that is a LastUserField (which stores the user who specified the change that is being tracked).

If I was starting from a blank model, I could just add an audit_log via:

from audit_log.models.managers import AuditLog
...
class SomeModel(models.Model)
    ...
    audit_log = AuditLog()

Applying this simple change and doing a schemamigration in django-south understandingly gives me an error:

 ! Cannot freeze field 'myapp.mymodelauditlogentry.action_user'
 ! (this field has class audit_log.models.fields.LastUserField)

 ! South cannot introspect some fields; this is probably because they are custom
 ! fields. If they worked in 0.6 or below, this is because we have removed the
 ! models parser (it often broke things).
 ! To fix this, read http://south.aeracode.org/wiki/MyFieldsDontWork

I read the MyFieldsDontWork wiki (and the Custom Fields/Introspection parts), but its not 100% clear what I need to do to get the fields to work.

I try adding:

from south.modelsinspector import add_introspection_rules
add_introspection_rules([], ["^audit_log\.models\.fields\.LastUserField"])

to my models.py which allowed the ./manage.py schemamigration to create a migration script with the previous error goes away. However when I try to migrate (to apply the migration), I get the following errors:

Running migrations for myapp:
 - Migrating forwards to 0004_auto__add_mymodelauditlogentry.
 > my_app:0004_auto__add_mymodelauditlogentry
Traceback (most recent call last):
  File "./manage.py", line 11, in <module>
    execute_manager(settings)
      File "/usr/local/lib/python2.6/dist-packages/Django-1.2.3-py2.6.egg/django/core/management/__init__.py", line 438, in execute_manager
    utility.execute()
  File "/usr/local/lib/python2.6/dist-packages/Django-1.2.3-py2.6.egg/django/core/management/__init__.py", line 379, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python2.6/dist-packages/Django-1.2.3-py2.6.egg/django/core/management/base.py", line 191, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/usr/local/lib/python2.6/dist-packages/Django-1.2.3-py2.6.egg/django/core/management/base.py", line 220, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/management/commands/migrate.py", line 105, in handle
    ignore_ghosts = ignore_ghosts,
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/__init__.py", line 191, in migrate_app
    success = migrator.migrate_many(target, workplan, database)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 221, in migrate_many
    result = migrator.__class__.migrate_many(migrator, target, migrations, database)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 292, in migrate_many
    result = self.migrate(migration, database)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 125, in migrate
    result = self.run(migration)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 93, in run
    south.db.db.current_orm = self.orm(migration)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 246, in orm
    return migration.orm()
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/utils.py", line 62, in method
    value = function(self)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/migration/base.py", line 422, in orm
    return FakeORM(self.migration_class(), self.app_label())
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/orm.py", line 46, in FakeORM
    _orm_cache[args] = _FakeORM(*args)  
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/orm.py", line 125, in __init__
    self.models[name] = self.make_model(app_label, model_name, data)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/orm.py", line 318, in make_model
    field = self.eval_in_context(code, app, extra_imports)
  File "/usr/local/lib/python2.6/dist-packages/South-0.7.3-py2.6.egg/south/orm.py", line 236, in eval_in_context
    return eval(code, globals(), fake_locals)
  File "<string>", line 1, in <module>
  File "/usr/local/lib/python2.6/dist-packages/django_audit_log-0.2.1-py2.6.egg/audit_log/models/fields.py", line 12, in __init__
    super(LastUserField, self).__init__(User, null = True, **kwargs)
TypeError: __init__() got multiple values for keyword argument 'null'

EDIT (12/20 noon): I can apply the schemamigration if I add the lines to models.py

from south.modelsinspector import add_introspection_rules, add_ignored_fields
add_ignored_fields(["^audit_log\.models\.fields\.LastUserField"])

except then the audit_log middleware doesn’t work as there is no action_user_id integer field in myapp_mymodelauditlogentry that references “auth_user” by “id”. Then I manually apply the SQL (sqlite syntax; obtained by using sqliteman on newly created database.)

ALTER TABLE "myapp_mymodelauditlogentry" ADD "action_user_id" integer REFERENCES "auth_user" ("id");

and it works. I’ll still give the bounty if someone explains how I’m supposed to do this in the context of django-south with migrations/introspection, without necessitating going to raw database dependent SQL and be grateful.

Also, I created an index for action_user_id. I notice that the normal creation of models with leads to an index called

CREATE INDEX "myapp_mymodelauditlogentry_26679921" ON "myapp_mymodelauditlogentry" ("action_user_id")

I hunted down that the hash 26679921 is created based on the field name with '%x' % (abs(hash(('action_user_id',))) % 4294967296L,) and isn’t based on anything else (so should always be _26679921 unless the database requires the long name to be trunctated). I’m not sure if the names of the index ever matter; but wanted to be safe.

Answer 1

Despite using the steps in @WoLpH’s answer, I still couldn’t create the migration. I had to modify the audit_log/models/fields.py file. Here’s how my LastUserField field looks like:

class LastUserField(models.ForeignKey):
    """ 
    A field that keeps the last user that saved an instance
    of a model. None will be the value for AnonymousUser.
    """

    def __init__(self, **kwargs):
        kwargs.pop('null', None)
        kwargs.pop('to', None)
        super(LastUserField, self).__init__(User, null = True, **kwargs)

    def contribute_to_class(self, cls, name):
        super(LastUserField, self).contribute_to_class(cls, name)
        registry = registration.FieldRegistry(self.__class__)
        registry.add_field(cls, self)

The following was added to my models.py file (which didn’t work) before I had to resort to doing this:

rules = [((fields.LastUserField,),
    [],    
    {   
        'to': ['rel.to', {'default': User}],
        'null': ['null', {'default': True}],
    },)]

# Add the rules for the `LastUserField`
add_introspection_rules(rules, ['^audit_log\.models\.fields\.LastUserField'])

Any suggestions on what I could do to avoid this hackery?