# fastapi.exceptions.RequestValidationError: field required

- **ID:** `python/fastapi-request-validation-missing-field`
- **Domain:** python
- **Category:** data_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Request body or query parameters missing a required field defined in Pydantic model or function signature.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **** (95% success)
   ```
   from fastapi import FastAPI, Request
from fastapi.exceptions import RequestValidationError
from fastapi.responses import JSONResponse

@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request: Request, exc: RequestValidationError):
    return JSONResponse(status_code=422, content={"detail": exc.errors()})
   ```
2. **** (90% success)
   ```
   Ensure required fields in Pydantic model: class Item(BaseModel):
    name: str  # no default
    price: float
   ```

## Dead Ends

- **** — FastAPI raises RequestValidationError specifically; generic catches miss it and return 500. (80% fail)
- **** — Hides bugs and may not satisfy API contract; still fails if type mismatch. (70% fail)