# pydantic_core._pydantic_core.ValidationError: 1 validation error for User
name
  字段必填 [type=missing, input_value={'age': 25}, input_type=dict]

- **ID:** `python/pydantic-v2-field-required-missing`
- **领域:** python
- **类别:** data_error
- **验证级别:** ai_generated
- **修复率:** 80%

## 根因

输入数据中缺少了必填字段。在 Pydantic v2 中，没有默认值的字段是必填的，传入缺少该字段的字典会抛出 missing 类型的 ValidationError。

## 版本兼容性

| 版本 | 状态 | 引入 | 弃用 |
|------|------|------|------|
| 2.x | active | — | — |

## 解决方案

1. **** (95% 成功率)
   ```
   Provide a default value: `name: str = ''` or `name: str = Field(default='unknown')`. Use `Optional[str] = None` if the field is genuinely optional.
   ```
2. **** (88% 成功率)
   ```
   Use model_validate with a pre-filled dict: `User.model_validate({'name': 'anon', **input_data})` so missing keys fall back to defaults.
   ```
3. **** (70% 成功率)
   ```
   Validate partial data with `User.model_construct(**input_data)` when you only need a best-effort object without validation.
   ```

## 无效尝试

- **** — Hides the real data problem; downstream code receives an incomplete or default object and fails later with confusing AttributeError (75% 失败率)
- **** — extra='allow' only affects unexpected fields, not missing required ones; the ValidationError persists (90% 失败率)