我在Django中有一些模型继承级别：

class WorkAttachment(models.Model):
    """ Abstract class that holds all fields that are required in each attachment """
    work            = models.ForeignKey(Work)
    added           = models.DateTimeField(default=datetime.datetime.now)
    views           = models.IntegerField(default=0)

    class Meta:
        abstract = True


class WorkAttachmentFileBased(WorkAttachment):
    """ Another base class, but for file based attachments """
    description     = models.CharField(max_length=500, blank=True)
    size            = models.IntegerField(verbose_name=_('size in bytes'))

    class Meta:
        abstract = True


class WorkAttachmentPicture(WorkAttachmentFileBased):
    """ Picture attached to work """
    image           = models.ImageField(upload_to='works/images', width_field='width', height_field='height')
    width           = models.IntegerField()
    height          = models.IntegerField()

WorkAttachmentFileBased和继承了许多不同的模型WorkAttachment。我想创建一个信号attachment_count，当创建附件时，该信号将更新父工作的字段。认为为父发件人（WorkAttachment）发出的信号也会在所有继承的模型上运行，这是合乎逻辑的，但事实并非如此。这是我的代码：

@receiver(post_save, sender=WorkAttachment, dispatch_uid="att_post_save")
def update_attachment_count_on_save(sender, instance, **kwargs):
    """ Update file count for work when attachment was saved."""
    instance.work.attachment_count += 1
    instance.work.save()

有没有办法使此信号对所有继承自其的模型起作用WorkAttachment？

Python 2.7，Django 1.4 pre-alpha

附言：我已经尝试了在网上找到的一种解决方案，但是它对我不起作用。