如何使用formencode验证器验证多个字段中至少有一个字段存在？

Question

对于Python Formencode验证器，有一个链式验证器RequireIfMissing和RequireIfPresent，它们允许给定其他字段的状态是否存在的要求。它似乎只适用于单个字段，这意味着如果缺少一个字段，需要另一个字段，或者如果存在一个字段，则需要另一个字段。如何至少需要一个字段？在

Answer 1

下面的类：RequireLeasstone将获得一个字段列表，并且仅当至少有一个字段存在时才会通过，如底部的成功和失败所示。在

from formencode import Schema, validators, Invalid
from formencode.validators import FormValidator


class RequireAtLeastOne(FormValidator):
    choices = []
    __unpackargs__ = ('choices',)
    def _convert_to_python(self, value_dict, state):
        for each in self.choices:
            if value_dict.get(each) is not None:
                return value_dict
        raise Invalid('You must give a value for %s' % repr(self.choices), value_dict, state)


class ValidateThings(Schema):
    field1 = validators.String(if_missing=None)    
    field2 = validators.String(if_missing=None)
    field3 = validators.String(if_missing=None)
    chained_validators = [RequireAtLeastOne(['field1', 'field2', 'field3'])]


""" Success """        
params = ValidateThings().to_python({"field2": 12})
params = ValidateThings().to_python({"field2": 12, "field3": 126})
params = ValidateThings().to_python({"field1": "foo", "field2": 12, "field3": 126})

""" Failure """
params = ValidateThings().to_python({})