python - 如何根据 James Bennett 的文章 "So you want a dynamic form"动态创建 ModelForm？

Question

James Bennett 的文章 "So you want a dynamic form" (2008 年 11 月 9 日)，他写道，要创建一个动态表单，您可以这样做:

def make_contact_form(user):
    fields = { 'name': forms.CharField(max_length=50),
               'email': forms.EmailField(),
               'message': forms.CharField(widget=forms.Textarea) }
    if not user.is_authenticated():
        fields['captcha'] = CaptchaField()
    return type('ContactForm', (forms.BaseForm,), { 'base_fields': fields })

但是您如何使用 forms.ModelForm 做同样的事情呢？

到目前为止，我只是在做这样的事情(我不知道如何将 type 与内部类“Meta”一起使用)

def make_order_edit_form(include_fields):
    class _OrderEditForm(forms.ModelForm):
        if 'fa_date' in include_fields:
            fa_date = CustomDateTimeField(label="first appointment time")

        class Meta:
            model = Order
            fields = include_fields
            widgets = custom_widgets

    return _OrderEditForm

其中 include_fields 是我要显示的字段元组。

然而，即使我编写了正确的 make_order_edit_form，我如何在 views.py 中使用它？具体如何将 POST 请求和订单实例传递给它？通常我会做类似的事情

order = Order.objects.get(pk=pk)

order_form = OrderEditForm(data=request.POST, instance=order)

奖励问题:

为什么 Bennett 使用 forms.BaseForm 而不是 forms.Form 创建一个 ContactForm？ (我假设这就是为什么这些字段也被称为 base_fields 的原因。)

Answer 1

make_order_edit_form 返回一个 ModelForm 类，因此您可以

form_cls = make_order_edit_form(fields)
order_form = form_cls(request.POST, instance=order)

加分题，查看Form代码:

class Form(BaseForm):
    "A collection of Fields, plus their associated data."
    # This is a separate class from BaseForm in order to abstract the way
    # self.fields is specified. This class (Form) is the one that does the
    # fancy metaclass stuff purely for the semantic sugar -- it allows one
    # to define a form using declarative syntax.
    # BaseForm itself has no way of designating self.fields.
    __metaclass__ = DeclarativeFieldsMetaclass

Form 有一个自定义元类 DeclarativeFieldsMetaclass，如果您在 中使用 Form，它会自动收集以声明语法编写的表单字段type()，看起来像(以 Bennett 为例)

type('ContactForm', (forms.Form,), {
    'name': forms.CharField(max_length=50),
    'email': forms.EmailField(),
    'message': forms.CharField(widget=forms.Textarea)}
# instead of
type('ContactForm', (forms.BaseForm,), { 'base_fields': fields })

更新

使用type构建ModelForm，没有太大区别

def make_order_edit_form(include_fields):
    d = {}
    class Meta:
        model = Order
        fields = include_fields
        widgets = custom_widgets 
    d = {'Meta':Meta}
    if 'fa_date' in include_fields:
        d['fa_date'] = CustomDateTimeField(label="first appointment time")
    return type('OrderEditForm', (forms.ModelForm,), d)