python type_error ai_generated true

pydantic.errors.PydanticUserError: @field_validator 'check_email' should be a classmethod or a staticmethod. Wrap the function with @classmethod or @staticmethod.

ID: python/pydantic-field-validator-signature-error

Also available as: JSON · Markdown · 中文
80%Fix Rate
90%Confidence
0Evidence
2024-03-15First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
2.x active — — —

Root Cause

In Pydantic v2, @field_validator must decorate a classmethod (or staticmethod). Missing the @classmethod decorator causes a PydanticUserError at class definition time.

generic

中文

在 Pydantic v2 中，@field_validator 必须装饰 classmethod（或 staticmethod）。缺少 @classmethod 装饰器会在类定义时引发 PydanticUserError。

Workarounds

  1. 98% success 
    from pydantic import BaseModel, field_validator

class User(BaseModel):
    email: str

    @field_validator('email')
    @classmethod
    def check_email(cls, v):
        assert '@' in v
        return v
  2. 95% success 
    from pydantic import BaseModel, field_validator

class User(BaseModel):
    email: str

    @field_validator('email')
    @staticmethod
    def check_email(v):
        return v.lower()

Dead Ends

Common approaches that don't work:

  1. 80% fail

    Decorator order matters: @field_validator must be the outermost decorator, i.e., listed first.

  2. 60% fail

    @validator is deprecated in v2 and raises PydanticDeprecatedSince20 warnings; it also still requires classmethod semantics.