def upload_images(instance, filename):
    filename = unique_filename(filename)
    return 'media/%s/%s' % (instance._meta.db_table, filename)
def upload_small_images_old(instance, filename):
    basename, format = filename.rsplit('.', 1)
    return 'media/%s/%s_small.%s' % (instance._meta.db_table, basename, format)
def upload_small_images(instance, filename):
    filename = unique_filename(filename)
    basename, format = filename.rsplit('.', 1)
    return 'media/%s/%s_small.%s' % (instance._meta.db_table, basename, format)

class Chapter(models.Model):
    title = models.CharField(max_length=255)
    image_id = models.ImageField(upload_to=upload_images)
    small_image_id = models.ImageField(upload_to=upload_small_images)
    is_published = models.IntegerField(max_length=1, default=0)
    node = models.ForeignKey(Node)
    def save(self, force_insert=False, force_update=False):
        if self.pk:
            try:
                old_obj = self.__class__.objects.get(pk=self.pk)
                if old_obj.image_id.path != self.image_id.path:
                    path = old_obj.image_id.path
                    filename = basename(path)
                    default_storage.delete(path)
                    default_storage.delete(upload_small_images_old(self, filename))
            except self.__class__.DoesNotExist:
                pass
        super(Chapter, self).save(force_insert=False, force_update=False)
        if force_insert and force_update:
            raise ValueError("Cannot force both insert and updating in "
                    "model saving.")
        new_path = self.image_id.path
        new_filename = basename(new_path)
        self.small_image_id = upload_small_images_old(self, new_filename)
        self.save_base(force_insert=force_insert, force_update=force_update)
        thumbnail(new_path)
    def __unicode__(self):
        return '<id>:%s; <title>:%s' % (self.id, self.title)
    def get_absolute_url(self):
        return '/%s/%i/' % (self.node.identifier, self.id)
    class Meta:
        db_table = 'chapter'
        verbose_name = 'Chapter'
        verbose_name_plural = 'Chapters'