python config_error ai_generated true

pydantic.errors.PydanticUserError：如果使用 `@field_validator` 且 `mode='after'`，函数必须为 classmethod。若想使用实例方法，请改用 `@model_validator(mode='after')`。

pydantic.errors.PydanticUserError: If you use `@field_validator` with `mode='after'`, the function must be a classmethod. If you want to use an instance method, use `@model_validator(mode='after')` instead.

ID: python/pydantic-field-validator-info-arg

其他格式: JSON · Markdown 中文 · English
80%修复率
88%置信度
0证据数
2024-03-05首次发现

版本兼容性

版本状态引入弃用备注
2.x active — — —

根因分析

实例方法被 @field_validator 装饰但未加 @classmethod，v2 对 after 模式不允许这样做。

English

An instance method was decorated with @field_validator without @classmethod, which v2 disallows for after-mode.

generic

解决方案

  1. 95% 成功率 
    from pydantic import BaseModel, field_validator
class M(BaseModel):
    x: int
    @field_validator('x', mode='after')
    @classmethod
    def check(cls, v):
        assert v > 0
        return v
  2. 90% 成功率 
    from pydantic import model_validator
class M(BaseModel):
    x: int
    @model_validator(mode='after')
    def check(self):
        assert self.x > 0
        return self

无效尝试

常见但无效的做法:

  1. 45% 失败

    Changes validation order; before-mode runs on raw input and may not see coerced types.

  2. 60% 失败

    Pydantic requires classmethod for field validators; staticmethod raises a different error.

  3. 55% 失败

    Bypasses validation pipeline and breaks model_validate paths.