问Django模型被保存，但不返回任何

EN

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

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>