Question

我正在考虑创建一个mixin表单类，以便我可以将一组通用字段添加到各种非常不同的表单中。只是将它用作基类是行不通的，因为我希望能够使用其他形式作为基类，如下所示：

class NoteFormMixin(object):
    note = forms.CharField()

class MainForm(forms.Form):
    name = forms.CharField()
    age = forms.IntegerField()

class SpecialForm(MainForm, NoteFormMixin):
    favorite_color = forms.CharField()

我唯一的问题是：这是如何运作的？到目前为止看起来如果我使用mixin，那么它无法识别mixin中设置的字段：

>>> ff1 = SpecialForm()
>>> ff1.fields
{'name': <django.forms.fields.CharField object at 0x178d3110>, 'age': <django.forms.fields.IntegerField object at 0x178d3190>, 'favorite_color': <django.forms.fields.CharField object at 0x178d3210>}

这只是无法做到的事情吗？

Answer 1

问题是你的NoteFormMixin派生自object而不是forms.Form。您需要将其更改为：

class NoteFormMixin(forms.Form):
    note = forms.CharField()

Answer 2

Patrick Altman的解决方案仅适用于常规表单 - 如果您使用ModelForm进行尝试，您将遇到元类冲突或某些字段缺失。

我找到的最简单和最简短的解决方案是附加到Django'ticket #7018 - 谢谢你， bear330 ：o）

你需要：

from django.forms.forms import get_declared_fields
. . .

class ParentsIncludedModelFormMetaclass(ModelFormMetaclass):
    """
        Thanks to bear330 - taken from https://code.djangoproject.com/attachment/ticket/7018/metaforms.py
    """

    def __new__(cls, name, bases, attrs):
        # We store attrs as ModelFormMetaclass.__new__ clears all fields from it
        attrs_copy = attrs.copy()
        new_class = super(ParentsIncludedModelFormMetaclass, cls).__new__(cls, name, bases, attrs)
        # All declared fields + model fields from parent classes
        fields_without_current_model = get_declared_fields(bases, attrs_copy, True)
        new_class.base_fields.update(fields_without_current_model)
        return new_class


def get_next_in_mro(current_class, class_to_find):
    """
        Small util - used to call get the next class in the MRO chain of the class
        You'll need this in your Mixins if you want to override a standard ModelForm method
    """
    mro = current_class.__mro__
    try:
        class_index = mro.index(class_to_find)
        return mro[class_index+1]
    except ValueError:
        raise TypeError('Could not find class %s in MRO of class %s' % (class_to_find.__name__, current_class.__name__))

然后你将mixin定义为通常的ModelForm，但是没有声明Meta ：

from django import forms
class ModelFormMixin(forms.ModelForm):

    field_in_mixin = forms.CharField(required=True, max_length=100, label=u"Field in mixin")
    . . .

    # if you need special logic in your __init__ override as usual, but make sure to
    # use get_next_in_mro() instead of super()
    def __init__(self, *args, **kwargs):
        #
        result = get_next_in_mro(self.__class__, ModelFormMixin).__init__(self, *args, **kwargs)

        # do your specific initializations - you have access to self.fields and all the usual stuff
        print "ModelFormMixin.__init__"

        return result

    def clean(self):
        result = get_next_in_mro(self.__class__, ModelFormMixin).clean(self)

        # do your specific cleaning
        print "ModelFormMixin.clean"

        return result

最后 - 最终的ModelForm，重用了ModelFormMixin的功能。你应该定义Meta和所有常用的东西。在最终形式中你可以称为超级（...）当你重写方法时（见下文）。

注意：最终格式必须将ParentsIncludedModelFormMetaclass设置为元类

注意：类的顺序很重要 - 将mixin放在第一位，然后放入ModelFrom。

class FinalModelForm(ModelFormMixin, forms.ModelForm):
    """
        The concrete form.
    """
    __metaclass__ = ParentsIncludedModelFormMetaclass

    class Meta:
        model = SomeModel

    field_in_final_form = forms.CharField(required=True, max_length=100, label=u"Field in final form")

    def clean(self):
        result = super(FinalModelForm, self).clean()

        # do your specific cleaning
        print "FinalModelForm.clean"

        return result

请记住，这只适用于两个类都是ModelForms的情况。如果你试图将Form和ModelFrom与这种技术混合搭配，它就不会很漂亮了：o）

Answer 3

class TextFormMixin(object):
    def __init__(self, *args, **kwargs):
        super(TextFormMixin, self).__init__(*args, **kwargs)
        self.fields['text'] = forms.CharField(widget=forms.Textarea, required=True)

    def clean_text(self):
        if not ('{{EMAIL}}' in self.cleaned_data.get('text', '')):
            raise ValidationError("You have to put {{EMAIL}} in message body.")
        return self.cleaned_data.get('text', '')

    def get_text(self):
        return self.cleaned_dat['text'].replace('{{EMAIL}}', self.case.get_email())


class NewCaseForm(TextFormMixin, forms.ModelForm):
    pass
class ReplyForm(TextFormMixin, forms.Form):
    to = forms.CharField(max_length=50)
    subject = forms.CharField(max_length=50)

Answer 4

只需澄清@Adam Dobrawy的回答，对我有帮助：

这不起作用：

class NoteFormMixin(object):
    note = forms.CharField()

这样做：

class NoteFormMixin(object):
    def __init__(self, *args, **kwargs):
        super(NoteFormMixin, self).__init__(*args, **kwargs)
        self.fields['note'] = forms.CharField()

此行为可能与django在类实例化期间收集字段的方式有关。.我没有费心去研究它的杂草。我只是发现这个花絮让我能够以一种易于阅读的方式编写我的mixin，而无需任何额外的特定于Django形式的操作。

使用带有Django表单类的mixin

4 个答案: