Django m2m 表单保存“通过”表

Question

我在保存包含“通过”类表的 m2m 数据时遇到问题。 我想将所有选定的成员（在表单中选择）保存在直通表中。 但我不知道如何在视图中初始化“通过”表。

我的代码：

class Classroom(models.Model):
     user = models.ForeignKey(User, related_name = 'classroom_creator')
     classname = models.CharField(max_length=140, unique = True)
     date = models.DateTimeField(auto_now=True)
     open_class = models.BooleanField(default=True)
     members = models.ManyToManyField(User,related_name="list of invited members", through = 'Membership')

class Membership(models.Model): 
      accept = models.BooleanField(User)
      date = models.DateTimeField(auto_now = True) 
      classroom = models.ForeignKey(Classroom, related_name = 'classroom_membership')
      member = models.ForeignKey(User, related_name = 'user_membership')

在视图中：

def save_classroom(request):
   classroom_instance = Classroom()
   if request.method == 'POST':
        form = ClassroomForm(request.POST, request.FILES, user = request.user) 
        if form.is_valid():
           new_obj = form.save(commit=False)
           new_obj.user = request.user 
           new_obj.save()
           membership = Membership(member = HERE SELECTED ITEMS FROM FORM,classroom=new_obj)

           membership.save() 

我应该如何初始化要填充的 Membership 表的成员资格？

Answer 1

您还需要为会员指定教室：

membership = Membership(member = request.user,
                        classroom=new_obj) #if new_obj if your classroom
membership.save()

我猜你也应该删除accept = models.BooleanField(User) 中的User。如果您使用auto_now，则无需在保存时设置日期！但也许 `auto_now_add 更可能是您需要的 (http://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.DateField)

Answer 2

如果使用正常的 m2m 关系（不是通过中间表），您可以替换：

membership = Membership(member = HERE SELECTED ITEMS FROM FORM,classroom=new_obj)
membership.save()

与

form.save_m2m()

但在使用中间表的情况下，您需要手动处理 POST 数据并创建包含所有必填字段的 Membership 对象 (similar problem)。最基本的解决方案是将您的视图更改为：

def save_classroom(request):
    if request.method == 'POST':
        form = ClassroomForm(request.POST, request.FILES)

        if form.is_valid():
           new_obj = form.save(commit=False)
           new_obj.user = request.user 
           new_obj.save()

           for member_id in request.POST.getlist('members'):
                membership = Membership.objects.create(member_id = int(member_id), classroom = new_obj)
           return HttpResponseRedirect('/')
    else:
        form = ClassroomForm()
    return render_to_response('save_classroom.html', locals())

注意 request.POST 是如何被操作的 (.getlist)。这是因为 post 和 get 是 QueryDict 对象，具有一些含义（request.POST['members'] 将始终返回一个对象！）。

您可以修改此代码以使其更可靠（错误处理等），更详细，例如：

member = get_object_or_404(User, pk = member_id)
membership = Membership.objects.create(member = member , classroom = new_obj)

但请注意，您正在循环中执行一些数据库查询，这通常不是一个好主意（就性能而言）。

Answer 3

这就是我在基于通用 UpdateForm 类的视图 (django 1.8) 中使用 form_valid 方法为类似但不同的应用程序所做的。

def form_valid(self, form):
    """
    If the form is valid, save the associated model.
    """
    self.object.members.clear()
    self.object = form.save(commit=False)
    self.object.user = self.request.user 
    self.object.save()

    list_of_members = form.cleaned_data['members']

    ClassRoom.objects.bulk_create([
            Membership(
                Course=self.object,
                member=member_person,
                order=num)
            for num, member_person in enumerate(list_of_members)
        ])
    return super(ModelFormMixin, self).form_valid(form)

Answer 4

和 dzida 一样，但是使用 form.cleaned_data 而不是 request.post：

def save_classroom(request):
    if request.method == 'POST':
        form = ClassroomForm(request.POST, request.FILES)

        if form.is_valid():
           new_obj = form.save(commit=False)
           new_obj.user = request.user
           new_obj.save()

           for member in form.cleaned_data['members'].all():
                Membership.objects.create(member = member,  classroom = new_obj)

           return HttpResponseRedirect('/')
    else:
        form = ClassroomForm()
    return render_to_response('save_classroom.html', locals())

您还需要考虑一些会员资格可能会被删除，所以：

def save_classroom(request):
    if request.method == 'POST':
        form = ClassroomForm(request.POST, request.FILES)

        if form.is_valid():
           new_obj = form.save(commit=False)
           new_obj.user = request.user
           new_obj.save()

           final_members = form.cleaned_data['members'].all()
           initial_members = form.initial['members'].all()

           # create and save new members
           for member in final_members:
                if member not in initial_members:
                    Membership.objects.create(member = member,  classroom = new_obj)

           # delete old members that were removed from the form
           for member in initial_members:
               if member not in final_members:
                   Membership.objects.filter(member = member, classroom = new_obj).delete()

           return HttpResponseRedirect('/')
    else:
        form = ClassroomForm()
    return render_to_response('save_classroom.html', locals())

如果您使用模型表单（例如在通用 CBV 中：form_class=ClassroomForm），请覆盖并将上面的保存逻辑放在 save 方法中，例如：

ClassroomForm(forms.ModelForm):
    members = ModelMultipleChoiceField(
        queryset=Classroom.objects.all(),
        widget=SelectMultiple
    )

    def save(self, commit=True):
        classroom = super().save(commit=False)
            if commit:
                classroom.save()
                if 'members' in self.changed_data:
                   final_members = self.cleaned_data['members'].all()
                   initial_members = self.initial['members']

                   # create and save new members
                   for member in final_members:
                        if member not in initial_members:
                            Membership.objects.create(member = member,  classroom = new_obj)

                   # delete old members that were removed from the form
                   for member in initial_members:
                       if member not in final_members:
                           Membership.objects.filter(member = member, classroom = new_obj).delete()

         return classroom