在 Django 中使用多表继承时是否可以直接设置隐式 OneToOne 键？

Question

我正在尝试通过多表继承来扩展库模型，这就是我最终得到的结果：

class CompetitionMedia(InstagramMedia):
    visible = models.BooleanField(default=True)
    most_creative = models.BooleanField(default=False)

@receiver(post_save, sender=InstagramMedia, dispatch_uid='create_competition_media')
def create_competition_media(sender, instance, created, **kwargs):
    competition_media = CompetitionMedia()
    competition_media.instagrammedia = instance
    competition_media.save() # fails

@receiver(post_save, sender=InstagramMedia, dispatch_uid='create_competition_media2')
def create_competition_media2(sender, instance, created, **kwargs):
    CompetitionMedia.objects.create(instagrammedia=instance) # Fails

可以这样做吗？

Answer 1

据我了解，您希望得到这样的东西：

class CompetitionMedia(models.Model):
    instagrammedia = models.OneToOneField(InstagramMedia, primary_key=True)
    visible = models.BooleanField(default=True)
    most_creative = models.BooleanField(default=False)

@receiver(post_save, sender=InstagramMedia, dispatch_uid='create_competition_media2')
def create_competition_media(sender, instance, created, **kwargs):
    if created:  
         CompetitionMedia.objects.create(instagrammedia=instance)

Answer 2

我显然应该设置parent_ptr，例如：

@receiver(post_save, sender=InstagramMedia, dispatch_uid='create_competition_media')
def create_competition_media2(sender, instance, created, **kwargs):
    if created:
        CompetitionMedia.objects.create(instagrammedia_ptr=instance)

但是，如果您先创建并保存父级然后尝试创建子级，则存在一个问题，即使在您未在子级中设置的字段上，子级也会覆盖父级。正如https://code.djangoproject.com/ticket/11618 和https://code.djangoproject.com/ticket/7623 中所述，所以我会避免它，因为它不是很明显会发生。

如果有人真的想走那条路，你需要这样做：

@receiver(post_save, sender=InstagramMedia, dispatch_uid='create_competition_media')
def create_competition_media2(sender, instance, created, **kwargs):
    if created:
        CompetitionMedia.objects.create(instagrammedia_ptr=instance)
        instance.save() # This should re-save the parent values.

更好：

@receiver(post_save, sender=InstagramMedia, dispatch_uid='create_competition_media')
def create_competition_media2(sender, instance, created, **kwargs):
    if created:
        CompetitionMedia.objects.create(instagrammedia_ptr=instance,
            **instance.__dict__)