Django模型已保存,但返回None

Question

我有一个模型管理器的简单模型:

class CompanyReviewManager(models.Manager):
    def get_votes_for_company(self, company):
        try:
            return CompanyReview.objects.filter(user = user).count()
        except ObjectDoesNotExist:
            return None

    def get_rating_for_field(self, installer, field):
        try:
            return CompanyReview.objects.filter(user = user).aggregate(Avg(field))
        except ObjectDoesNotExist:
            return None

class CompanyReview(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL)
    satisfaction = models.PositiveSmallIntegerField(blank = True, null = True,)
    comments = models.TextField(blank = True, null = True,)

    objects = CompanyReviewManager()

    def save(self, *args, **kwargs):
        obj = super(InstallerReview, self).save(*args, **kwargs)
        return obj

当我现在尝试在Django shell中保存一个对象时,该对象将被保存,但不会返回任何内容.为什么？

In [1]: company_obj = InstallerReview()
In [2]: company_obj.user = CompanyUser.objects.all()[2]
In [3]: obj = company_obj.save()
In [4]: obj
Out[4]: 
In [5]: company_obj
Out[5]: <CompanyReview: AdminCompany>

为什么第3步失败没有错误？

Answer 1

因为超类save方法不返回任何内容.它不需要:self正在被保存,没有必要返回别的东西并调用它obj.

你可以self从你的子类save方法返回,但没有多大意义.通常在Python中,如果函数就地更改对象,则它们不会返回已更改的对象:与list sort()方法进行比较.