# fastapi.exceptions.RequestValidationError: 字段必填

- **ID:** `python/fastapi-validation-error-field-required`
- **领域:** python
- **类别:** type_error
- **验证级别:** ai_generated
- **修复率:** 80%

## 根因

请求体或查询参数中缺少必填字段。

## 版本兼容性

| 版本 | 状态 | 引入 | 弃用 |
|------|------|------|------|
| 3.x | active | — | — |

## 解决方案

1. **Add default values or make fields optional** (90% 成功率)
   ```
   class Item(BaseModel):
    name: str = 'default'  # optional with default
    price: float = 0.0
   ```
2. **Use Pydantic's Field with alias** (85% 成功率)
   ```
   class Item(BaseModel):
    item_name: str = Field(..., alias='name')
# Request uses 'name', model uses 'item_name'
   ```

## 无效尝试

- **Providing field with None value** — FastAPI treats None as missing for required fields. (70% 失败率)
- **Using wrong field name due to case sensitivity** — Field names are case-sensitive in Pydantic models. (60% 失败率)