后端经常使用 Form 作表单验证, 但是你知道
- 表单中的键值是怎么绑定到 Field 上的?
- Field 中的 validators, filters, default 调用顺序是什么?
要想回答以上问题, 就需要从源码说起.
先上伪源码为敬
class UnboundField(object):
⑨def bind(self, form, name, ...):
return self.field_class(*self.args, **kw)
class DefaultMeta(object):
⑧def bind_field(self, form, unbound_field, options):
return unbound_field.bind(form=form, **options)
class Field(object):
def __new__(cls, *args, **kwargs):
⑩if '_form' in kwargs and '_name' in kwargs:
return super(Field, cls).__new__(cls)
①else: # 扫描到 name = StringField
return UnboundField(cls, *args, **kwargs)
⑪def __init__(self, *args, **kwargs):
pass
def process(self, formdata, data=unset_value):
if data is unset_value:
设置 default
if formdata is not None:
有 key 时, default 所做的工作付诸东流
self.data = filter(self.data)
def validate(self, form, extra_validators=tuple()):
itertools.chain(self.validators, extra_validators)
class FormMeta(type):
②def __init__(cls, name, bases, attrs): # DemoForm 定义完毕
type.__init__(cls, name, bases, attrs)
cls._unbound_fields = None
cls._wtforms_meta = None
③def __call__(cls, *args, **kwargs): # DemoForm(...)
设置 cls._unbound_fields
设置 cls._wtforms_meta
class BaseForm(object):
⑥def __init__(self, ...):
for:
⑦field = meta.bind_field(self, unbound_field, options)
def process(self, formdata=None, obj=None, data=None, **kwargs):
obj 和 (data, kwargs) 不含 name 时调用 field.process(formdata)
def validate(self, extra_validators=None):
field.validate(self, extra)
def with_metaclass(meta, base=object):
return meta("NewBase", (base,), {})
class Form(with_metaclass(FormMeta, BaseForm)):
④def __init__(self, formdata=None, ...): # 初始化 DemoForm(args)
⑤super(Form, self).__init__(self._unbound_fields, meta=meta_obj, prefix=prefix)
self.process(formdata, obj, data=data, **kwargs)
def validate(self):
收集 extra
return super(Form, self).validate(extra)
一言不合举例子
class DemoForm(Form):
name = StringField("name", validators=[DataRequired()], filters=(), default=None)
form = DemoForm(args)
form.validate()
- 扫描到 name = StringField, 调用 Field.
__new__ - DemoForm 定义完毕, 调用元类
FormMeta.__init__ - 遇到 form = DemoForm(args) 时:
- 先调用 元类
FormMeta.__call__ - 再调用
Form.__init__, 继而触发每个Field.process
- 运行
form.validate()最终会调用到每个Field.validate