Mix in fields to django model form.

gistfile1.py

"""
Mix in fields to django model form.
"""

from django.conf import settings
settings.configure()

from django import forms
from django.db import models


class Model(models.Model):
    some_data = models.CharField(max_length=100)
    some_extra = models.CharField(max_length=100)

    class Meta:
        app_label = 'test'


class AMixin(object):
    __metaclass__ = forms.forms.DeclarativeFieldsMetaclass

    a = forms.CharField(max_length=50)


class BMixin(object):
    __metaclass__ = forms.forms.DeclarativeFieldsMetaclass

    b = forms.CharField(max_length=50)


class ModelForm(forms.ModelForm):
    class Meta:
        model = Model
        fields = ['some_data']

    def save(self, *args, **kwargs):
        cleaned_data = self.clean()

        # Do real save instead of this
        print 'cleaned_data', cleaned_data
        Model(
            some_data=cleaned_data['some_data'],
            some_extra='%s%s' % (cleaned_data['a'], cleaned_data['b'])
        )


class ModelFormMetaclassWithMixins(
    forms.forms.DeclarativeFieldsMetaclass,
    forms.models.ModelFormMetaclass
):
    def __new__(cls, name, bases, attrs):

        # new form with fields from ModelForm
        new_class = super(ModelFormMetaclassWithMixins, cls).__new__(
            cls, name, bases, attrs
        )

        # mixins waiting to be mixin
        mixins = [
            b for b in bases
            if type(b) == forms.forms.DeclarativeFieldsMetaclass
        ]

        # mixin fields waiting to be mixin
        mixin_fields = forms.forms.get_declared_fields(mixins, attrs, True)

        # mix in new fields
        new_class.base_fields.update(mixin_fields)

        return new_class


def get_form(name, mixins, model_form):
    bases = [model_form]
    bases.extend(mixins)

    new_class = ModelFormMetaclassWithMixins(name, tuple(bases), {})

    return new_class


data = {
    'some_data': 'some_data_post',
    'a': 'a_post',
    'b': 'b_post'
}

form = get_form('MyForm', [AMixin, BMixin], ModelForm)(initial=data)
print 'fields',  form.fields
print form.as_p()

form = get_form('MyForm', [AMixin, BMixin], ModelForm)(data)

if form.is_valid():
    form.save()