python data_error ai_generated true

fastapi.exceptions.RequestValidationError: 1 validation error for Item name field required (type=value_error.missing)

ID: python/fastapi-422-field-required

Also available as: JSON · Markdown · 中文
80%Fix Rate
89%Confidence
0Evidence
2024-05-02First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.x active — — —

Root Cause

The Pydantic model declares a required field, but the incoming JSON body does not include it, so request parsing fails before the handler runs.

generic

中文

Pydantic 模型声明了一个必填字段，但传入的 JSON 请求体中没有该字段，因此在处理函数运行之前请求解析就失败了。

Workarounds

  1. 95% success 
    class Item(BaseModel):
    name: str = ''
  2. 93% success 
    from typing import Optional
class Item(BaseModel):
    name: Optional[str] = None

Dead Ends

Common approaches that don't work:

  1. 90% fail

    Validation happens in FastAPI's dependency layer before the handler, so the except never triggers.

  2. 80% fail

    This affects output serialization, not input validation.