Django m2m表单保存"直通"表

Question

我在保存m2m数据方面遇到了麻烦,其中包含一个"通过"类表.我想在直通表中保存所有选定的成员(在表单中选择).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')

并在视图中:

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() 

我应该如何初始化成员资格表的成员资格？

Answer 1

如果使用正常m2m关系(不通过中间表),您可以替换:

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

同

form.save_m2m()

但是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(类似问题).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())

请注意如何操作request.POST(.getlist).这是因为post和get是QueryDict对象,它们有一些含义(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),并且更详细,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(在性能方面).

Answer 2

就像dzida所做的一样，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())

您还需要考虑一些成员资格可能会被删除，因此：

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())

如果使用模型形式（例如在通用CBV：中form_class=ClassroomForm），请覆盖保存逻辑并将其放在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