def dynamic_upload_to(self, filename):
    folder_name = 'file/%s/%s' % (datetime.datetime.now().strftime("%Y/%m/%d"), self.sub_matter.pk)
    file_name = os.path.normpath(get_valid_filename(os.path.basename(filename)))
    return os.path.join(folder_name, file_name)


@python_2_unicode_compatible
class File(NotificationObjectMixin, MPTTModel, SubMatterRelatedModelMixin, TimeStampedModel):
    LOCAL = 'lc'

    user = models.ForeignKey('users.User', related_name='folders', null=True, blank=True)
    parent = TreeForeignKey('self', null=True, blank=True, related_name='children')
    name = models.CharField(max_length=255, null=True, blank=False)

    is_dir = models.BooleanField(default=True)

    #File's fileds
    token = models.ForeignKey('Token', related_name='folders', null=True, blank=True)
    type = models.CharField(max_length=2, choices=deepcopy(TYPE_CHOICES).append((LOCAL, _('Local'))), default=LOCAL)
    file = models.FileField(max_length=255, upload_to=dynamic_upload_to, null=True, blank=True)
    backend_id = models.CharField(max_length=1024, null=True, blank=True)
    mime_type = models.CharField(max_length=255, default='pekama/directory', blank=True)
    size = models.CharField(max_length=125, default='0', blank=True)