wtforms，在构造函数中生成字段

Question

我需要在表单的构造函数中生成我的字段，因为所需字段的数量可能会有所不同。我认为我目前的解决方案是问题所在。当我尝试在模板中扩展表单时出现异常，说

AttributeError: 'UnboundField' 对象没有属性 'call'

这段代码有什么问题？

class DriverTemplateSchedueForm(Form):
    def __init__(self, per_day=30, **kwargs):
        self.per_day = per_day
        ages = model.Agency.query.all()
        ages = [(a.id, a.name) for a in ages]
        self.days = [[[]] * per_day] * 7
        for d in range(7):
            for i in range(per_day):
                lbl = 'item_' + str(d) + '_' + str(i)
                self.__dict__[lbl] = SelectField(lbl, choices=ages)
                self.days[d][i] = self.__dict__[lbl]
        for day in self.days:
            print(day)

        Form.__init__(self, **kwargs)

Answer 1

修复

您需要将字段添加到您的 class 而不是您的 instance：

def driver_template_schedue_form(ages, per_day=30, **kwargs):
    """Dynamically creates a driver's schedule form"""

    # First we create the base form
    # Note that we are not adding any fields to it yet
    class DriverTemplateScheduleForm(Form):
        pass

    # Then we iterate over our ranges
    # and create a select field for each
    # item_{d}_{i} in the set, setting each field
    # *on our **class**.
    for d in range(7):
        for i in range(per_day):
            label = 'item_{:d}_{:d}'.format(d, i)
            field = SelectField(label, choices=ages)
            setattr(DriverTemplateScheduleForm, label, field)

    # Finally, we return the *instance* of the class
    # We could also use a dictionary comprehension and then use
    # `type` instead, if that seemed clearer.  That is:
    # type('DriverTemplateScheduleForm', Form, our_fields)(**kwargs)
    return DriverTemplateScheduleForm(**kwargs)

为什么向self 添加字段不起作用？

WTForms 使用元类将表单和字段注册在一起并保持顺序。 *Field 实例是未绑定创建的，added to the Form class' _unbound_fields attribute 并绑定到类实例 when the class is being constructed by the meta-class。

DriverTemplateScheduleForm.__init__ 运行时，_unbound_fields 已被填充。您可以将您的字段推送到self._unbound_fields，并且事情也可以正常工作，但这是使用私有API，因此以后可能会中断。

Answer 2

关于元类的答案是正确的，但如果你真的需要这个（就像我一样）：

class SomeForm(Form):
    def __init__(self, *args, **kwargs):
        for name in kwargs.keys():
            if name.startswith('PREFIX_'):
                field = HiddenField()
                setattr(self, name, field)
                self._unbound_fields = self._unbound_fields + [[name, field]]
        super(SomeForm, self).__init__(*args, **kwargs)

请注意，我们不会修改_unbound_fields，下次不会在表单类中包含此字段。