将 mixin 与 Django 表单类一起使用

Question

我正在考虑创建一个 mixin 表单类，以便可以将一组通用字段添加到各种不同的表单中。仅将其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：这是如何工作的？到目前为止，如果我使用 mixin，那么它就无法识别从该 mixin 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>}

这只是不能做的事情吗？

Answer 1

问题是您的 NoteFormMixin 是从 object 而不是 forms.Form 派生的。你需要把它改成这样：

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

Answer 2

Patrick Altman 的解决方案仅适用于 常规 表单 - 如果您尝试使用 ModelForm 进行此操作，您将遇到元类冲突或缺少某些字段。

我发现的最简单和最短的解决方案是 Django 的附件ticket #7018 - 谢谢，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__))

然后你将你的 mixin 定义为一个普通的 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 的特性。 您应该定义 Meta 和所有常见的东西。在最终形式中，您可以调用 super(...) 当您覆盖方法时（见下文）。

注意：最终表单必须将 ParentsIncludedModelFormMetaclass 设置为元类

注意：类的顺序很重要 - 将 mixin 放在首位，然后是 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，这仅在两个类都是 ModelForms 时才有效。如果您尝试使用这种技术混合和匹配 Form 和 ModelFrom，它根本不会漂亮: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

只是对@Adam Dobrawy 的回答提供了一些明确性，这对我有帮助：

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()

这种行为可能与 django 在类实例化期间如何收集字段或其他东西有关.. 我没有费心去研究它。我刚刚发现这个花絮可以让我以可读性好的方式编写我的 mixin，而无需任何额外的 django-form-specific crud。