问使用flask-admin，我如何获得一个支持不存在的标签的标签字段？

EN

class CustomTagField(Select2TagsField):

    widget = CustomTagWidget(multiple=True)

    def pre_validate(self, form):
        pass

    def process_formdata(self, valuelist):
        if valuelist:
            self.data = []
            for tagname in valuelist:
                rv = Tag.query.filter_by(name=tagname).first()
                if rv:
                    self.data.append(rv)
                else:
                    self.data.append(Tag(name=tagname))
        else:
            self.data = []

    def iter_choices(self):

        self.blank_text = ""

        tags = list(set([str(tag.name) for tag in Tag.query.all()]))
        model_tags = [tag.name for tag in self.object_data]

        self.choices = [[tag, tag] for tag in tags]

        # Yield empty object in order to have an empty placeholder
        yield (u'__None', self.blank_text, self.data is None)

        for value, label in self.choices:
            yield (value, label, value in model_tags)

class CustomTagWidget(widgets.Select):
    def __call__(self, field, **kwargs):
        kwargs.setdefault('data-tags', '1')
        # Or call select2 in tags mode

        allow_blank = getattr(field, 'allow_blank', False)
        if allow_blank and not self.multiple:
            kwargs['data-allow-blank'] = u'1'

        return super(CustomTagWidget, self).__call__(field, **kwargs)

form_extra_fields = {
        'tags': CustomTagField(
            'Tags',
        ),
}

$('#tags').select2({
  tags: true,
});