如何在选定的多个字段之间传递数据？

Question

我对Flask和WTForms还不熟悉，一直在为这个简单的任务而努力。我想显示选项列表。用户可以选择多个选项，然后这些选项生成一个新的可选选项列表。你知道吗

为了简化目前的情况，我只是尝试直接从一个SelectMultipleField中获取所选的选项，并将它们设置为第二个SelectMultipleField中的选项：

class SelForm(FlaskForm):
    choices = []
    selections = SelectMultipleField('Available Streams', choices=choices)
    submit = SubmitField('Choose Streams')

@streams_blueprint.route('/select', methods=['GET','POST'])
def select():
    # Grab a selectable list of studies from database.
    form = SelForm()
    db_objects = [(stream.id, stream.name) for stream in Stream.objects()]
    form.selections.choices = db_objects
    if form.validate_on_submit():
        form2 = SelForm()
        selections = form.selections.data
        form2.selections.choices = selections
    else:
        form2 = SelForm()
    return render_template('select_streams.html', form=form, form2=form2)

不管我怎么做，表单总是以初始状态呈现（form.selections.choices=db_objects和form2.selections.choices=[]）。validate_on_submit段什么也不做。如何在单击“提交”后更新form2？你知道吗

Answer 1

整个周末我都在绞尽脑汁，终于找到了答案。问题是SelectMultipleField中的默认验证器实际上不起作用。如果我用is_submitted替换validate_on_submit，代码就会运行。此版本符合我的要求：

@streams_blueprint.route('/select', methods=['GET','POST'])
def select():
    # Grab a selectable list of studies from database.
    form = SelForm()
    db_objects = [(stream.id, stream.name) for stream in Stream.objects()]
    form.selections.choices = db_objects
    if form.is_submitted():
        form2 = SelForm()
        selections = form.selections.data
        new_objects = [(stream.id, stream.name) for stream in Stream.objects(id__in=selections)]
        form2.selections.choices = new_objects
    else:
        form2 = SelForm()
    return render_template('select_streams.html', form=form, form2=form2)

如果我需要验证器，我将不得不为此字段类型编写自定义验证器。你知道吗