original_type = field.type_
    if is_dataclass(original_type) and hasattr(original_type, "__pydantic_model__"):
        original_type = original_type.__pydantic_model__
    use_type = original_type
    if lenient_issubclass(original_type, BaseModel):
        original_type = cast(Type[BaseModel], original_type)
        use_type = cloned_types.get(original_type)
        if use_type is None:

In this case, the original path `/app` would actually be served at `/api/v1/app`.

Even though all your code is written assuming there's just `/app`.

```Python hl_lines="6"
{!../../../docs_src/behind_a_proxy/tutorial001.py!}
```

This time, it will overwrite the method `APIRoute.get_route_handler()`.

This method returns a function. And that function is what will receive a request and return a response.

Here we use it to create a `GzipRequest` from the original request.

```Python hl_lines="18-26"
{!../../../docs_src/custom_request_and_route/tutorial001.py!}
```

!!! note "Technical Details"

We can declare all that without having to modify the original `APIRouter` by passing those parameters to `app.include_router()`:

```Python hl_lines="14-17" title="app/main.py"
{!../../../docs_src/bigger_applications/app/main.py!}
```

There are some scenarios where you might want to override a dependency during testing.

You don't want the original dependency to run (nor any of the sub-dependencies it might have).

Instead, you want to provide a different dependency that will be used only during tests (possibly only some specific tests), and will provide a value that can be used where the value of the original dependency was used.

### Use cases: external service

```

`CORSMiddleware` 에서 사용하는 기본 매개변수는 제한적이므로, 브라우저가 교차-도메인 상황에서 특정한 출처, 메소드, 헤더 등을 사용할 수 있도록 하려면 이들을 명시적으로 허용해야 합니다.

다음의 인자들이 지원됩니다:

* `allow_origins` - 교차-출처 요청을 보낼 수 있는 출처의 리스트입니다. 예) `['https://example.org', 'https://www.example.org']`. 모든 출처를 허용하기 위해 `['*']` 를 사용할 수 있습니다.
* `allow_origin_regex` - 교차-출처 요청을 보낼 수 있는 출처를 정규표현식 문자열로 나타냅니다.  `'https://.*\.example\.org'`.

    But if you have custom headers that you want a client in a browser to be able to see, you need to add them to your CORS configurations ([CORS (Cross-Origin Resource Sharing)](cors.md){.internal-link target=_blank}) using the parameter `expose_headers` documented in <a href="https://www.starlette.io/middleware/#corsmiddleware" class="external-link" target="_blank">Starlette's CORS docs</a>.

s" class="external-link" target="_blank">Verwenden Sie dafür das Präfix 'X-'</a>.

    Wenn Sie jedoch benutzerdefinierte Header haben, die ein Client in einem Browser sehen soll, müssen Sie sie zu Ihrer CORS-Konfigurationen ([CORS (Cross-Origin Resource Sharing)](cors.md){.internal-link target=_blank}) hinzufügen, indem Sie den Parameter `expose_headers` verwenden, der in der <a href="https://www.starlette.io/middleware/#corsmiddleware" class="external-link" target="_blank">Starlette-CO...

### The callback path expression

The callback *path* can have an <a href="https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.1.0.md#key-expression" class="external-link" target="_blank">OpenAPI 3 expression</a> that can contain parts of the original request sent to *your API*.

In this case, it's the `str`:

* Grundlegende Startmodelle für Benutzer (ändern und entfernen Sie nach Bedarf).
* **Alembic**-Migrationen.
* **CORS** (Cross Origin Resource Sharing).
* **Celery**-Worker, welche Modelle und Code aus dem Rest des Backends selektiv importieren und verwenden können.