python type_error ai_generated true

PydanticUserError: `@validator` cannot be applied to instance methods

ID: python/fastapi-pydantic-v1-v2-migration-validator

Also available as: JSON · Markdown · 中文
80%Fix Rate
88%Confidence
0Evidence
2024-03-06First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
2.x active — — —

Root Cause

Code migrated to Pydantic v2 but still uses `@validator` without `@classmethod`, or uses removed v1 APIs.

generic

中文

代码迁移到 Pydantic v2 后仍使用 `@validator` 且未加 `@classmethod`，或使用了已移除的 v1 API。

Workarounds

  1. 95% success 
    from pydantic import field_validator
class M(BaseModel):
    x: int
    @field_validator('x')
    @classmethod
    def check(cls, v):
        return v
  2. 90% success 
    @validator('x')
@classmethod
def check(cls, v): ...

Dead Ends

Common approaches that don't work:

  1. 60% fail

    Blocks FastAPI updates and other deps; temporary only.

  2. 90% fail

    Unrelated to validator decorator usage.