ValueError: Cannot import the required field 'null_fields.Key'

[Ash]

OK, yeah, I read the wiki page on extending the introspection and
still wasn't able to get it to work.

I've got the following simple subclass of some of the base Django
fields:

# File is eve.lib.null_fields
class Key(models.ForeignKey):
def __init__(self, *args, **kwargs):
kwargs['null'] = True
kwargs['blank'] = True
return super(Key, self).__init__(*args, **kwargs)

And I added the following to my main urls.py:

from south.modelsinspector import add_introspection_rules
add_introspection_rules(rules=[], patterns=["^eve\.lib\.null_fields"])

But yet I still get the error about not being able to import it.

What am I missing?

Oh, and please add a note to the wiki page suggesting that you add
this block to urls.py, as it took me a while to figure that out. The
docs arn't very user-centric.

[Thomas Guettler]

Ash wrote:
> OK, yeah, I read the wiki page on extending the introspection and
> still wasn't able to get it to work.
>
> I've got the following simple subclass of some of the base Django
> fields:
>
> # File is eve.lib.null_fields
> class Key(models.ForeignKey):
> def __init__(self, *args, **kwargs):
> kwargs['null'] = True
> kwargs['blank'] = True
> return super(Key, self).__init__(*args, **kwargs)
>
> And I added the following to my main urls.py:
>
> from south.modelsinspector import add_introspection_rules
> add_introspection_rules(rules=[], patterns=["^eve\.lib\.null_fields"])
>
> But yet I still get the error about not being able to import it.

Did you recreate the migration file? Is the import statement at the top?

> Oh, and please add a note to the wiki page suggesting that you add
> this block to urls.py, as it took me a while to figure that out. The
> docs arn't very user-centric.

Yes, I think the documentation could be improved. Here are some things
that could be added:
- Simple example how to add a field that just subclasses from a django field.
- Where should the add_introspection_rules() call happen?

It would be better if the Exception would happen during creation of the migration
file, and not during executing it.

Thomas

--
Thomas Guettler, http://www.thomas-guettler.de/
E-Mail: guettli (*) thomas-guettler + de

[Andrew Godwin]

You have to re-generate the affected migration for the change to take effect; it
changes what's written in the migration file (startmigration), not how it's
applied (migrate).

Andrew

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[Ash]

Either I'm more lost than I thought, or you think I made it further
than I did.

I was able to run the migrate_to_south command for the app involved,
but this error is stopping me from making my migration.

I'm running: './migrate.py startmigration user skill_queue --auto',
and that's when it fails. So I don't have a migration file to
recreate. I think... (Nothing in user actually uses the null_field
fields, but they have ForeignKey relations to a different app that
isn't under South's control that does call null_fields.) It would also
be nice if South didn't demand to be able to import field types that
are not actually used in the app it's managing migrations for.

[Andrew Godwin]

Apologies; import errors with introspection issues are nearly always
done during the migrate step. What's the exact error traceback?

Andrew

[Ash]

./manage.py startmigration user skill_queue --auto
Logging started.
Traceback (most recent call last):
File "./manage.py", line 11, in <module>
execute_manager(settings)
File "/usr/local/lib/python2.6/dist-packages/django/core/management/
__init__.py", line 362, in execute_manager
utility.execute()
File "/usr/local/lib/python2.6/dist-packages/django/core/management/
__init__.py", line 303, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/usr/local/lib/python2.6/dist-packages/django/core/management/
base.py", line 195, in run_from_argv
self.execute(*args, **options.__dict__)
File "/usr/local/lib/python2.6/dist-packages/django/core/management/
base.py", line 222, in execute
output = self.handle(*args, **options)
File "/usr/local/lib/python2.6/dist-packages/South-0.6.2-py2.6.egg/
south/management/commands/startmigration.py", line 237, in handle
last_orm = migrations[-1].orm
File "/usr/local/lib/python2.6/dist-packages/South-0.6.2-py2.6.egg/
south/orm.py", line 62, in __get__
self.orm = FakeORM(*self._args)
File "/usr/local/lib/python2.6/dist-packages/South-0.6.2-py2.6.egg/
south/orm.py", line 45, in FakeORM
_orm_cache[args] = _FakeORM(*args)
File "/usr/local/lib/python2.6/dist-packages/South-0.6.2-py2.6.egg/
south/orm.py", line 106, in __init__
self.models[name] = self.make_model(app_name, model_name, data)
File "/usr/local/lib/python2.6/dist-packages/South-0.6.2-py2.6.egg/
south/orm.py", line 282, in make_model
field = self.eval_in_context(code, app, extra_imports)
File "/usr/local/lib/python2.6/dist-packages/South-0.6.2-py2.6.egg/
south/orm.py", line 206, in eval_in_context
raise ValueError("Cannot import the required field '%s'" % value)
ValueError: Cannot import the required field 'null_fields.Key'

[Ash]

In the end, I went back to using deseb. I hope that in time South will
improve to the point where it's useful for me.