Base64 Encoded Field with south support

base64field.py

#-*- coding: utf-8 -*-
# Work in progress. The South part does not work correctly yet!

import base64
from django.db import models

# Stolen from http://djangosnippets.org/snippets/1669/
class Base64Field(models.TextField):

    def contribute_to_class(self, cls, name):
        if self.db_column is None:
            self.db_column = name
        self.field_name = name + '_base64'
        super(Base64Field, self).contribute_to_class(cls, self.field_name)
        setattr(cls, name, property(self.get_data, self.set_data))

    def get_data(self, obj):
        return base64.decodestring(getattr(obj, self.field_name))

    def set_data(self, obj, data):
        setattr(obj, self.field_name, base64.encodestring(data))

try:
    from south.modelsinspector import add_introspection_rules
    add_introspection_rules(
        [([Base64Field],[],{})],
        ["^database_email_backend\.fields\.Base64Field"]
    )
except ImportError:
    pass

south_frozen_model.py

# model field:
content = Base64Field(null=True, blank=True, default=None)

# frozen south data on first migration (creating the table with the base63 field)

{'content_base64': ('database_email_backend.fields.Base64Field', [], {'default': 'None', 'null': 'True', 'db_column': "'content'", 'blank': 'True'}),}

# running the first migration works fine, but adding another migration fails with

# ./bin/django schemamigration database_email_backend --auto

Traceback (most recent call last):
  File "./bin/django", line 27, in <module>
    djangoprojectrecipe.manage.main('project.settings.base')
  File "/Users/stefanfoulis/.buildout/eggs/djangoprojectrecipe-1.1.1-py2.7.egg/djangoprojectrecipe/manage.py", line 18, in main
    utility.execute()
  File "/Users/stefanfoulis/.buildout/eggs/Django-1.3-py2.7.egg/django/core/management/__init__.py", line 379, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/stefanfoulis/.buildout/eggs/Django-1.3-py2.7.egg/django/core/management/base.py", line 191, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/Users/stefanfoulis/.buildout/eggs/Django-1.3-py2.7.egg/django/core/management/base.py", line 220, in execute
    output = self.handle(*args, **options)
  File "/Users/stefanfoulis/.buildout/eggs/South-0.7.3-py2.7.egg/south/management/commands/schemamigration.py", line 123, in handle
    name = change_source.suggest_name()
  File "/Users/stefanfoulis/.buildout/eggs/South-0.7.3-py2.7.egg/south/creator/changes.py", line 73, in suggest_name
    for change_name, params in self.get_changes():
  File "/Users/stefanfoulis/.buildout/eggs/South-0.7.3-py2.7.egg/south/creator/changes.py", line 178, in get_changes
    old_fields, old_meta, old_m2ms = self.split_model_def(self.old_orm[key], self.old_defs[key])
  File "/Users/stefanfoulis/.buildout/eggs/South-0.7.3-py2.7.egg/south/creator/changes.py", line 31, in split_model_def
    elif isinstance(model._meta.get_field_by_name(name)[0], models.ManyToManyField):
  File "/Users/stefanfoulis/.buildout/eggs/Django-1.3-py2.7.egg/django/db/models/options.py", line 311, in get_field_by_name
    % (self.object_name, name))
django.db.models.fields.FieldDoesNotExist: Attachment has no field named 'content_base64'