gistfile1.py

class FolderManager(models.Manager):
    # so that we can do Folder.objects...
    def get_query_set(self):
        return super(FolderManager, self).get_query_set().filter(is_folder=True)


class Folder(Item):
    '''
    this class is kind of funny looking because Items cannot have
    a ForeignKey field pointing to a subclass of itself.
    '''
    objects = FolderManager()

    def __init__(self, *args, **kwargs):
        # override the default behavior of the is_folder field
        self._meta.get_field('is_folder').default = True
        super(Folder, self).__init__(*args, **kwargs)

    class Meta:
        # don't create a table
        proxy = True