尝试在动态 WTForm 字段中插入空白选项

Question

我试图根据我在 SOF here 上找到的结果在现有的工作动态字段（客户）中添加一个空白选项，但是出现错误。

错误是ValueError: invalid literal for int() with base 10: ''.

如有必要，我可以提供完整的回溯。

这是表格 - 如您所见，动态字段是客户：

class FilterWorkorderForm(FlaskForm):
    id = IntegerField('id', validators=[Optional()])
    date = DateField('Date', validators=[Optional()])
    customer = SelectField('Customer', coerce=int, validators=[Optional()])
    customer_po = StringField('Customer PO', validators=[Optional()])
    requested_by = StringField('Requested By', validators=[Optional()])
    work_description = StringField('Work Description', validators=[Optional()])
    status = SelectField('Status', choices=[('Quote', 'Quote'), ('Pending', 'Pending'), ('WIP', 'WIP'), ('Complete', 'Complete'), ('TBI', 'TBI'), ('Invoiced', 'Invoiced'), ('VOID', 'VOID')])

路线如下：

@app.route('/reports/filter_workorder', methods=['GET', 'POST'])
@login_required
def filter_workorder():
    results = None
    form = FilterWorkorderForm()
    form.customer.choices = [(cus.id, cus.company_name) for cus in Company.query.order_by('id')]
    ### LINE CAUSING ERROR ### form.customer.choices.insert(0, ("", "")) ### LINE CAUSING ERROR ###
    if request.method == 'POST':
        if form.validate_on_submit():
            try:
                customer_id = form.customer.data
                customer = Company.query.filter_by(id = customer_id).first_or_404()
                customer_name = customer.company_name
                filter_data = {'id' : form.id.data, 'date' : form.date.data, 'customer_po' : form.customer_po.data, 'customer' : customer_name, 
                'work_description' : form.work_description.data, 'status' : form.status.data}
                filter_data = {key: value for (key, value) in filter_data.items() if value}
                results = Workorder.query.filter_by(**filter_data).all()
            except Exception as e:
                db.session.rollback()
                flash(e)
        return render_template('filter_workorder.html', form = form, results = results)
    return render_template('filter_workorder.html', form = form)

Answer 1

问题在于使用整数强制转换呈现您的表单，特别是客户字段。

根据 WTForms's documentation on the Select widget:

The field must provide an iter_choices() method which the widget will call on rendering; this method must yield tuples of (value, label, selected).

如果你看the source code for this method：

def iter_choices(self):
    for value, label in self.choices:
        yield (value, label, self.coerce(value) == self.data)

此方法中没有针对强制转换失败的异常处理。在您的情况下，self.coerce(value) 作为 int('') 执行，这会导致您遇到 ValueError 异常。

至少有两种解法：

移除coerce.
使用 sentinel value 例如 0 或 -1 表示没有客户被选中：
```
form.customer.choices.insert(0, (0, ""))
```
该值将通过强制转换，但您需要处理该值（以取消设置 "customer" 字段）post 表单处理。

尝试在动态 WTForm 字段中插入空白选项

Trying to insert blank option in dynamic WTForm field

python

flask

wtforms

flask-wtforms