多对多关系的内联表单集的挂件

Question

根据Kevin Dias在这篇文章中的说明，我尝试为两个相关的模型生成一个表单。这在一对多的关系中似乎可以正常工作，但在多对多的关系中我遇到了问题。

下面是一个关于用户和角色管理的示例代码：

#models.py
from django.db import models

class Role(models.Model): # for each role there can be multiple users
    role_name=models.CharField(max_length=20)

class User(models.Model): # each user can have multiple roles
    name=models.CharField(max_length=20)
    role=models.ManyToManyField(Role, through='UserRole')

class UserRole(models.Model): # table to store which user has which roles
    role=models.ForeignKey(Role)
    user=models.ForeignKey(User)

# forms.py
from django.forms import ModelForm
from django.forms.models import inlineformset_factory

from rightmanagement.models import Role, User

class UserForm(ModelForm):
    class Meta:
        model = User

RoleFormSet = inlineformset_factory(User, Role) # this is probably the line that causes the problem

# views.py
from django.http import HttpResponseRedirect
from rightmanagement.models import User
from rightmanagement.forms import RoleFormSet, UserForm

# Create view
from django.views.generic import CreateView
class UserCreate(CreateView):
    model = User
    form_class = UserForm

    def get(self, request, *args, **kwargs):
        """
        Handles GET requests and instantiates blank versions of the form
        and its inline formsets.
        """
        self.object = None
        form_class = self.get_form_class()
        form = self.get_form(form_class)
        role_form = RoleFormSet()
        return self.render_to_response(
            self.get_context_data(form=form,
                                  role_form=role_form))

    def post(self, request, *args, **kwargs):
        """
        Handles POST requests, instantiating a form instance and its inline
        formsets with the passed POST variables and then checking them for
        validity.
        """
        self.object = None
        form_class = self.get_form_class()
        form = self.get_form(form_class)
        role_form = RoleFormSet(self.request.POST)
        if (form.is_valid() and role_form.is_valid()):
            return self.form_valid(form, role_form)
        else:
            return self.form_invalid(form, role_form)

    def form_valid(self, form, role_form):
        """
        Called if all forms are valid. Creates a Recipe instance along with
        associated Ingredients and Instructions and then redirects to a
        success page.
        """
        self.object = form.save()
        role_form.instance = self.object
        role_form.save()
        return HttpResponseRedirect(self.get_success_url())

    def form_invalid(self, form, role_form):
        """
        Called if a form is invalid. Re-renders the context data with the
        data-filled forms and errors.
        """
        return self.render_to_response(
            self.get_context_data(form=form,
                                  role_form=role_form))

这些设置导致了错误信息：<class 'rightmanagement.models.Role'> has no ForeignKey to <class 'rightmanagement.models.User'>。

经过一些研究，我发现了这个链接：Django inlineformset_factory 和 ManyToMany 字段。看起来，内联表单集只适用于ForeignKey，而不适用于ManyToManyField。另外，文档也可以这样理解。

不过，我觉得在这个特定的情况下，使用外键而不是多对多关系是没有意义的。对于多对多关系，Django内置的内联表单集应该是什么样子的呢？目标是构建一个表单，允许将用户分配给已经存在的角色，或者在角色不存在时创建新角色并将其分配给用户。

django 模型管理外键多对多关系数据库关系用户角色表单生成内联表单集

多对多关系的内联表单集的挂件

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