删除用作外键的对象

I have next models:

我有下一个型号：

class Target(models.Model):
    name = models.CharField(max_length=100, blank=False)


class SubTarget(models.Model):
    target = models.ForeignKey(Target, related_name='sub_targets')
    name = models.CharField(max_length=100, blank=True, null=True, default='')
class Target(m