django - 当 commit=False 时，Django 表单 save() 方法中是否需要 save_m2m() ？

Question

文档似乎非常坚定地表明情况确实如此......

https://docs.djangoproject.com/en/dev/topics/forms/modelforms/#the-save-method

我特别提到了这一部分:

Another side effect of using commit=False is seen when your model has a many-to-many relation with another model. If your model has a many-to-many relation and you specify commit=False when you save a form, Django cannot immediately save the form data for the many-to-many relation. This is because it isn't possible to save many-to-many data for an instance until the instance exists in the database.

To work around this problem, every time you save a form using commit=False, Django adds a save_m2m() method to your ModelForm subclass. After you've manually saved the instance produced by the form, you can invoke save_m2m() to save the many-to-many form data.

我对 django 还很陌生，昨天偶然发现了这个信息。

但是，我有一个观点，我不调用 save_m2m() 方法，但它实际上保存了 m2m 数据。

这是我的观点:

class SubscriberCreateView(AuthCreateView):
    model = Subscriber
    template_name = "forms/app.html"
    form_class = SubscriberForm
    success_url = "/app/subscribers/"

    def get_form_kwargs(self):
        kwargs = super(SubscriberCreateView, self).get_form_kwargs()
        kwargs.update({'user': self.request.user})
        return kwargs

    def form_valid(self, form):
        self.object = form.save(commit=False)
        self.object.user = self.request.user
        try:
            self.object.full_clean()
        except ValidationError:
            form._errors["email"] = ErrorList([u"This subscriber email is already in your account."])
            return super(SubscriberCreateView, self).form_invalid(form)
        return super(SubscriberCreateView, self).form_valid(form)

我的模型:

class Subscriber(models.Model):

    STATUS_CHOICES = (
        (1, ('Subscribed')),
        (2, ('Unsubscribed')),
        (3, ('Marked as Spam')),
        (4, ('Bounced')),
        (5, ('Blocked')),
        (6, ('Disabled')),
    )

    user = models.ForeignKey(User)
    status = models.IntegerField(('status'), choices=STATUS_CHOICES, default=1)
    email = models.EmailField()
    subscriber_list = models.ManyToManyField('SubscriberList')
    first_name = models.CharField(max_length=70, blank=True)
    last_name = models.CharField(max_length=70, blank=True)
    phone = models.CharField(max_length=20, blank=True)
    facebook_id = models.CharField(max_length=40, blank=True)
    twitter_id = models.CharField(max_length=40, blank=True)
    address1 = models.CharField(max_length=100, blank=True)
    address2 = models.CharField(max_length=100, blank=True)
    postcode = models.CharField(max_length=10, blank=True)
    city = models.CharField(max_length=30, blank=True)
    country = models.CharField(max_length=30, blank=True)
    date_joined = models.DateTimeField(auto_now_add=True)
    date_updated = models.DateTimeField(auto_now=True)

    class Meta:
        unique_together = (
            ('user', 'email',),
        )
    
    def __unicode__(self):
        return self.email

我的表格:

class SubscriberForm(ModelForm):
    def __init__(self, user, *args, **kwargs):
        super (SubscriberForm, self).__init__(*args, **kwargs)
        self.fields['subscriber_list'].queryset = SubscriberList.objects.filter(user=user)
    
    class Meta:
        model = Subscriber
        exclude = ('user', 'facebook_id', 'twitter_id')

那为什么我的观点有效呢？ (这意味着，表单中某一字段的 m2m 关系实际上是在处理表单时保存的。)

Answer 1

父类之一正在执行模型对象及其 m2m 关系的完整保存。我不能确定，因为我没有 AuthCreateView 的声明，但命名约定表明它源于“CreateView”。如果是这样，您的 View 的继承将如下所示:SubscriberCreateView -> AuthCreateView -> CreateView -> BaseCreateView -> ModelFormMixin。 ModelFormMixin 有一个 form_valid() 方法，您(可能)使用 super() 调用该方法。

这是完整的method从 Django 1.4 开始:

def form_valid(self, form):
    self.object = form.save()
    return super(ModelFormMixin, self).form_valid(form)

所以你已经得到它了。然而，让我指出一些潜在的困惑。 @Wogan 很聪明地指出你没有保存你的对象。按照您的代码的方式，您使用未保存的模型实例进行验证，然后它被丢弃，因为 ModelFormMixin 重新分配 self.object。

1. 这意味着如果您稍后访问 self.object，它可能不是您所期望的。
2. 您丢失了 self.object.user 信息。 (因为 user 是模型上的必填字段，并且您在表单中将其排除，所以我预计 save() 会失败。因此父级 AuthCreateView 一定在做某事。当然，它可能正在处理整个 save() 并且根本不会命中 ModelFormMixin。)

为了避免这种困惑，只需不要将您的实例分配给 self.object 即可。也许: validate_obj = form.save(commit=False)