///

/// tip | "Tipp"

Juste du **Python** standard.

Par exemple, pour un `int`:

```Python
item_id: int
```

ou pour un modèle `Item` plus complexe :

```Python
item: Item
```

... et avec cette déclaration unique, vous obtenez :

* Une assistance dans votre IDE, notamment :
    * la complétion.

### `RequestValidationError` vs `ValidationError`

/// warning | "警告"

如果您觉得现在还用不到以下技术细节，可以先跳过下面的内容。

///

`RequestValidationError` 是 Pydantic 的 <a href="https://docs.pydantic.dev/latest/concepts/models/#error-handling" class="external-link" target="_blank">`ValidationError`</a> 的子类。

**FastAPI** 调用的就是 `RequestValidationError` 类，因此，如果在 `response_model` 中使用 Pydantic 模型，且数据有错误时，在日志中就会看到这个错误。

    full_name = user_dict["full_name"],
    disabled = user_dict["disabled"],
    hashed_password = user_dict["hashed_password"],
)
```

/// info | "说明"

`user_dict` 的说明，详见[**更多模型**一章](../extra-models.md#user_indict){.internal-link target=_blank}。

///

## 返回 Token

`token` 端点的响应必须是 JSON 对象。

响应返回的内容应该包含 `token_type`。本例中用的是**Bearer**Token，因此， Token 类型应为**`bearer`**。

                // drop through...
            } catch (final LinkageError e) {
                // drop through...
            }
        }

        try {
            // last chance - classic model
            return Class.forName(name);
        } catch (final Exception e) {
            throw new TypeNotPresentException(name, e);
        } catch (final LinkageError e) {

                Arguments.of(true, new String[] {"--force-interactive", "--non-interactive", "--batch-mode"}, false),
                Arguments.of(false, new String[] {"--non-interactive"}, true),
                Arguments.of(false, new String[] {"--batch-mode"}, true),
                Arguments.of(false, new String[] {"--non-interactive", "--batch-mode"}, true));
    }

inside and make sure it is serializable as JSON, using the same [JSON Compatible Encoder](../tutorial/encoder.md){.internal-link target=_blank} explained in the tutorial. This is what allows you to return **arbitrary objects**, for example database models.

But if you are certain that the content that you are returning is **serializable with JSON**, you can pass it directly to the response class and avoid the extra overhead that FastAPI would have by passing your return content through the...

It can't handle nested models very well. So, if the JSON body in the request is a JSON object that has inner fields that in turn are nested JSON objects, it cannot be properly documented and validated.

/// check | "Inspired **FastAPI** to"

///

/// tip

### Concurrency + Parallelism: Web + Machine Learning

With **FastAPI** you can take advantage of concurrency that is very common for web development (the same main attraction of NodeJS).