django自定义Field实现一个字段存储以逗号分隔的字符串

from django import formsfrom django.db import modelsfrom django.utils.text import capfirstfrom django.core import exceptions

class MultiSelectFormField(forms.MultipleChoiceField):    widget = forms.CheckboxSelectMultiple

    def __init__(self, *args, **kwargs):        self.max_choices = kwargs.pop('max_choices', 0)        super(MultiSelectFormField, self).__init__(*args, **kwargs)

    def clean(self, value):        if not value and self.required:            raise forms.ValidationError(self.error_messages['required'])        # if value and self.max_choices and len(value) > self.max_choices:        #     raise forms.ValidationError('You must select a maximum of %s choice%s.'        #             % (apnumber(self.max_choices), pluralize(self.max_choices)))        return value

class MultiSelectField(models.Field):    __metaclass__ = models.SubfieldBase

    def get_internal_type(self):        return "CharField"

    def get_choices_default(self):        return self.get_choices(include_blank=False)

    def _get_FIELD_display(self, field):        value = getattr(self, field.attname)        choicedict = dict(field.choices)

    def formfield(self, **kwargs):        # don't call super, as that overrides default widget if it has choices        defaults = {'required': not self.blank, 'label': capfirst(self.verbose_name),                    'help_text': self.help_text, 'choices': self.choices}        if self.has_default():            defaults['initial'] = self.get_default()        defaults.update(kwargs)        return MultiSelectFormField(**defaults)

    def get_prep_value(self, value):        return value

    def get_db_prep_value(self, value, connection=None, prepared=False):        if isinstance(value, basestring):            return value        elif isinstance(value, list):            return ",".join(value)

    def to_python(self, value):        if value is not None:            return value if isinstance(value, list) else value.split(',')        return ''

    def contribute_to_class(self, cls, name):        super(MultiSelectField, self).contribute_to_class(cls, name)        if self.choices:            func = lambda self, fieldname = name, choicedict = dict(self.choices): ",".join([choicedict.get(value, value) for value in getattr(self, fieldname)])            setattr(cls, 'get_%s_display' % self.name, func)

    def validate(self, value, model_instance):        arr_choices = self.get_choices_selected(self.get_choices_default())        for opt_select in value:            if (int(opt_select) not in arr_choices):  # the int() here is for comparing with integer choices                raise exceptions.ValidationError(self.error_messages['invalid_choice'] % value)        return

    def get_choices_selected(self, arr_choices=''):        if not arr_choices:            return False        list = []        for choice_selected in arr_choices:            list.append(choice_selected[0])        return list

    def value_to_string(self, obj):        value = self._get_val_from_obj(obj)        return self.get_db_prep_value(value)