How to use the briefcase.models.DocumentType function in briefcase

def test_unknown_type(self):
        document_type = DocumentType.unknown_type()
        self.assertEqual(document_type.mimetype, "application/octet-stream")
        self.assertEqual(document_type.name, "Unknown type")

def render(self, context):
        document_types = DocumentType.objects.exclude(extension__exact='').order_by('extension')
        context[self.as_varname] = document_types
        return ''

Forces a JOIN to DocumentType and User models.
        
        Cannot be achieved by setting list_select_related=True, because
        the foreign key fields have null=True. We have an OUTER JOIN here.
        """
        qs = super(DocumentAdmin, self).queryset(request)
        return qs.select_related('type', 'added_by')

    def save_model(self, request, obj, form, change):
        if not change:
            obj.added_by = request.user
        super(DocumentAdmin, self).save_model(request, obj, form, change)


admin.site.register(DocumentStatus, DocumentStatusAdmin)
admin.site.register(DocumentType, DocumentTypeAdmin)
admin.site.register(Document, DocumentAdmin)

mimetype = mimetype or "application/octet-stream"
        obj, created = cls.objects.get_or_create(extension=extension,
                                                 mimetype=mimetype)
        if created:
            obj.name = extension.upper() + ' Document'
            obj.save()
        return obj


class Document(models.Model):
    u"""
    The document itself.
    """
    # Basic document data.
    file = models.FileField(verbose_name=_("file"), upload_to='uploads/%Y/%m/%d/', help_text=_("This is the document itself - well, just a file."))
    type = models.ForeignKey(DocumentType, verbose_name=_("document type"), blank=True, null=True, help_text=_("Document type, for example 'Microsoft Word Document' or 'PDF File'."))
    # Meta-information.
    status      = models.ForeignKey(DocumentStatus, verbose_name=_("document status"), null=True, blank=True)
    added_by    = models.ForeignKey(User, verbose_name=_("added by"), null=True, blank=True, editable=False)
    added_at    = models.DateTimeField(_("added at"), auto_now_add=True)
    updated_at  = models.DateTimeField(_("recently changed at"), auto_now=True)

    class Meta:
        verbose_name = _("Document")
        verbose_name_plural = _("Documents")
        ordering = ['-added_at']

    def __unicode__(self):
        return os.path.basename(self.file.name)

    def save(self, *args, **kwargs):
        u"""

A very thin wrapper for the generic ``object_list`` view.
    
    Currently we supply here only the ``template_object_name`` argument, but
    more functionality may come and it is good to keep the generic document
    list in one place.
    This also allows for a greater customization by setting some view arguments
    in the URLconf.
    
    Template receives a ``document_list`` context variable which is a QuerySet
    instance.
    """
    extra_context = kwargs.pop('extra_context', {})
    if extension is not None:
        # we could get around without this query for DocumentType,
        # but we want the type object to be accessible in the template
        document_type = get_object_or_404(DocumentType, extension__exact=extension.lower())
        extra_context['document_type'] = document_type
        queryset = queryset.filter(type=document_type)
    if 'template_object_name' not in kwargs:
        kwargs['template_object_name'] = 'document'
    return object_list(request, queryset, template_name=template_name, extra_context=extra_context, **kwargs)