Select multiple using a manytomany checkbox

from django import oldforms
from django.db import models
from django.utils.functional import curry

class CheckBoxManyToMany(models.ManyToManyField):
    def get_manipulator_field_objs(self):
        if self.rel.raw_id_admin:
            return [oldforms.RawIdAdminField]
        else:
            choices = self.get_choices_default()
            return [curry(oldforms.CheckboxSelectMultipleField, choices=choices)]

    def get_manipulator_fields(self, opts, manipulator, change, name_prefix='', rel=False, follow=True):
        """
        Returns a list of oldforms.FormField instances for this field. It
        calculates the choices at runtime, not at compile time.

        name_prefix is a prefix to prepend to the "field_name" argument.
        rel is a boolean specifying whether this field is in a related context.
        """
        field_objs, params = self.prepare_field_objs_and_params(manipulator, name_prefix)

        # BooleanFields (CheckboxFields) are a special case. They don't take
        # is_required.
        if 'is_required' in params:
            del params['is_required']

        # Finally, add the field_names.
        field_names = self.get_manipulator_field_names(name_prefix)
        return [man(field_name=field_names[i], **params) for i, man in enumerate(field_objs)]