AttributeError: '' object has no attribute '_set'

Question

如果有人能帮助我，我会很高兴。

我想做的是：在删除作者后，将所有 "votes" 更改为零。

class Author(models.Model):
    """Model representing an author."""

    first_name = models.CharField(max_length=100)
    last_name = models.CharField(max_length=100)
    date_of_birth = models.DateField(null=True, blank=True)
    date_of_death = models.DateField('died', null=True, blank=True)

    class Meta:
        ordering = ['last_name', 'first_name']

    def get_absolute_url(self):
        """Returns the url to access a particular author instance."""
        return reverse('catalog:author-detail', args=[str(self.id)])

    def __str__(self):
        """String for representing the Model object."""
        return '{0}, {1}'.format(self.last_name, self.first_name)


class Option(models.Model):
    def default_votes():
        d=Author.objects.all().first()
        print(dir(d))
        for a in d.option_set.all():
            a.votes=0
    author = models.ForeignKey(Author, on_delete=models.SET_DEFAULT, default=default_votes())
    choice_text = models.CharField(max_length=200)
    votes = models.IntegerField(default=0)

    def __str__(self):
        return self.choice_text

但我得到：

  File "C:\Users\chainsaw\Desktop\django-locallibrary-tutorial-master\django-loc
allibrary-tutorial-master\catalog\models.py", line 128, in default_votes
    for a in d.option_set.all():
AttributeError: 'Author' object has no attribute 'option_set'

但是在shell中有这个属性。我可以改变它。我做错了什么？

Answer 1

您已将 default 值设置为 default=default_votes() 因为 不是 "callable function"，Django 在创建迁移文件期间采用函数的结果。

因此，将默认参数设置为可调用函数（仅提供函数，不带括号）

author = models.ForeignKey(Author, on_delete=models.SET_DEFAULT, <b>default=default_votes</b>)

注意： 你的函数 default_votes 不是 return 任何东西，所以，return "appropriate value(s)" 来自函数.

Answer 2

小问题是您实际上不应该调用您的默认函数；只需删除 ():

author = models.ForeignKey(Author, on_delete=models.SET_DEFAULT, default=default_votes)

AttributeError: '' object has no attribute '_set'

AttributeError: '' object has no attribute '_set'

python

django

shell

django-queryset

AttributeError: '***' object has no attribute '***_set'

AttributeError: '***' object has no attribute '***_set'

python

django

shell

django-queryset

AttributeError: '' object has no attribute '_set'

AttributeError: '' object has no attribute '_set'