pydantic验证器Validator

---

title: pydantic验证器Validator
date: 2020-01-17T01:20:38.127Z
tags: python,pydantic
categories: python

最近学习Python的fastapi框架，发现使用了pydantic来做输入参数。看了一下pydantic的文档，发现也可以用来做验证器。
一开始用的挺好，后来碰到一个多字段联合验证的情况，在文档里翻了一下，发现可以这么用，

from pydantic import BaseModel, ValidationError, validator
class UserModel(BaseModel):
    name: str
    username: str
    password1: str
    password2: str

    @validator('name')
    def name_must_contain_space(cls, v):
        if ' ' not in v:
            raise ValueError('must contain a space')
        return v.title()

    #联合验证
    @validator('password2')
    def passwords_match(cls, v, values, **kwargs):
        if 'password1' in values and v != values['password1']:
            raise ValueError('passwords do not match')
        return v

    @validator('username')
    def username_alphanumeric(cls, v):
        assert v.isalpha(), 'must be alphanumeric'
        return v

print(UserModel(name='samuel colvin', username='scolvin', password1='zxcvbn',
                password2='zxcvbn'))
#> name='Samuel Colvin' username='scolvin' password1='zxcvbn' password2='zxcvbn'

try:
    UserModel(name='samuel', username='scolvin', password1='zxcvbn',
              password2='zxcvbn2')
except ValidationError as e:
    print(e)
"""
2 validation errors for UserModel
name
  must contain a space (type=value_error)
password2
  passwords do not match (type=value_error)
"""

于是动手试了一下，结果却失败了。经过一番调试，发现，这个values，并不是所有的输入参数，只有验证通过的才有，并且不包括当前的参数，当前参数从v取。