Django M2M表单保存“通过”表

Question

我在保存包含“直通”类表的m2m数据时遇到了麻烦。我想将所有选定的成员（在表单中选择）保存在通过表中。但是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() 

我应该如何初始化要正确填充的Membership表的成员资格？

Answer 1

如果使用正常的m2m关系（不通过中间表），则可以替换：

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

与

form.save_m2m()

但是，在使用中间表的情况下，你需要手动处理POST数据并创建具有所有必填字段的Membership对象（类似问题）。最基本的解决方案是将视图更改为：

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是具有某些含义的QueryDict对象（request.POST [‘members’]将始终返回一个对象！）。

你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)

但是请注意，你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）。