python - 保存 m2m 关系的 Django 问题

Question

我过去能够保存与表单的 m2m 关系，但我目前遇到以下问题，我不明白为什么:

# models.py

class File(models.Model):
    client = models.ManyToManyField(Client)
    product = models.ForeignKey(Product, related_name='item_product')
    created = models.DateTimeField(default=datetime.now)
    created_by = models.ForeignKey(User)

# forms.py

class FileForm(ModelForm):

    class Meta:
        model = File
        exclude = ('client')

    def CustomSave(self,product,client,user):
        temp = self.save(commit=False)
        temp.product = product
        temp.client = client   # < ?!?!
        temp.created_by = user
        temp.save()
        temp.save_m2m()
        return temp

# views.py

def new_client_view(request):

    if request.method == 'POST':
        try:
            i_product = int(request.POST['product'])
        except ValueError:
            raise Http404()
        # get a 'product' from the POST data
        p = Product.objects.get(id=i_product)

        formFile = FileForm(p, request.POST, auto_id='f_%s')
        formItemData = ItemDataForm(p, request.POST, auto_id='i_%s')

        if formFile.is_valid() and formItemData.is_valid():
            c = Client()
            c.save()
            tempFile = formFile.CustomSave(p,c,request.user)
            tempItem = ItemForm().CustomSave(tempFile,request.user)
            formItemData.CustomSave(tempItem,request.user)
            return redirect(client_view, c.id)
        else:
            return render_to_response('newClient.html', {'error':'The form was not valid'}, context_instance=RequestContext(request))
     else:
        return render_to_response('newClient.html', {}, context_instance=RequestContext(request))

当我尝试上面的方法时，我得到:

'File' instance needs to have a primary key value before a many-to-many relationship can be used.

django 指出错误来自 temp.client = client

我尝试了 CustomSave 的各种排列，但都没有成功 :(

有什么想法吗？

Answer 1

您正在尝试将一个客户端分配给 ManyToMany 字段。如果它是客户端的 ForeignKey，这将起作用，但对于 ManyToMany，您将必须执行如下操作:

temp.client.add(client)

注意:必须先保存temp，然后才能分配客户。这是因为 Django 使用一个表将客户端映射到文件，如果该文件最初不存在，则无法添加带有空键的行。查看 Django 生成的表结构应该有助于理清思路。