And your **FastAPI** application might also be composed of several files/modules, etc.

### **FastAPI** app file { #fastapi-app-file }

Let's say you have a file structure as described in [Bigger Applications](bigger-applications.md):

```
.
├── app
│   ├── __init__.py
│   └── main.py
```

In the file `main.py` you have your **FastAPI** app:


{* ../../docs_src/app_testing/app_a_py310/main.py *}

```mermaid
sequenceDiagram
    participant App
    participant Client

    App->>App: Produce Item 1
    App->>Client: Send Item 1
    App->>App: Produce Item 2
    Client->>Client: Process Item 1
    App->>Client: Send Item 2
    App->>App: Produce Item 3
    Client->>Client: Process Item 2
    App->>Client: Send Item 3
    Client->>Client: Process Item 3
    Note over App: Keeps producing...

	registerCommand(serverCmd)
	registerCommand(fmtGenCmd)

	// Set up app.
	cli.HelpFlag = cli.BoolFlag{
		Name:  "help, h",
		Usage: "show help",
	}
	cli.VersionPrinter = printMinIOVersion

	app := cli.NewApp()
	app.Name = name
	app.Author = "MinIO, Inc."
	app.Version = ReleaseTag
	app.Usage = "High Performance Object Storage"

from fastapi.testclient import TestClient

app = FastAPI()

items = {}


@app.on_event("startup")
async def startup_event():
    items["foo"] = {"name": "Fighters"}
    items["bar"] = {"name": "Tenders"}


@app.get("/items/{item_id}")
async def read_items(item_id: str):
    return items[item_id]


def test_read_items():
    with TestClient(app) as client:
        response = client.get("/items/foo")

경로 접두사가 제거(stripped)되는 프록시가 있다는 것은, 코드에서는 `/app`에 경로를 선언하지만, 위에 한 겹(프록시)을 추가해 **FastAPI** 애플리케이션을 `/api/v1` 같은 경로 아래에 두는 것을 의미합니다.

이 경우 원래 경로 `/app`은 실제로 `/api/v1/app`에서 서비스됩니다.

코드는 모두 `/app`만 있다고 가정하고 작성되어 있는데도 말입니다.

{* ../../docs_src/behind_a_proxy/tutorial001_py310.py hl[6] *}

///

### Pydantic v1 und v2 in derselben App { #pydantic-v1-and-v2-on-the-same-app }

Es wird von Pydantic **nicht unterstützt**, dass ein Pydantic‑v2‑Modell Felder hat, die als Pydantic‑v1‑Modelle definiert sind, und umgekehrt.

```mermaid
graph TB
    subgraph "❌ Nicht unterstützt"

        activityHelper.login(OptionalThing.empty());
        assertEquals(
                "{\"@timestamp\":\"2022-01-01T00:00:00.000Z\",\"log.level\":\"INFO\",\"ecs.version\":\"1.2.0\",\"service.name\":\"fess\",\"event.dataset\":\"app\",\"process.thread.name\":\"main\",\"log.logger\":\"org.codelibs.fess.helper.ActivityHelperTest$1\",\"labels.action\":\"LOGIN\",\"labels.user\":\"-\",\"labels.permissions\":\"-\"}",
                localLogMsg.get());

        asyncpg.pgroto.pgproto.UUID behaves"""
        raise TypeError("vars() argument must have __dict__ attribute")


def test_pydanticv2():
    from pydantic import field_serializer

    app = FastAPI()

    @app.get("/fast_uuid")
    def return_fast_uuid():
        asyncpg_uuid = MyUuid("a10ff360-3b1e-4984-a26f-d3ab460bdb51")
        assert isinstance(asyncpg_uuid, uuid.UUID)

async_callable_gen_dependency = AsyncCallableGenDependency()
methods_dependency = MethodsDependency()


@app.get("/partial-function-dependency")
async def get_partial_function_dependency(
    value: Annotated[
        str, Depends(partial(function_dependency, "partial-function-dependency"))
    ],
) -> str:
    return value


@app.get("/partial-async-function-dependency")
async def get_partial_async_function_dependency(

    return data


@router_default.post("/items/")
async def router_default_post(data: dict):
    return data


app.include_router(router_lax)
app.include_router(router_strict)
app.include_router(router_default)

client = TestClient(app)


def test_lax_router_on_strict_app_accepts_no_content_type():
    response = client.post("/lax/items/", content='{"key": "value"}')
    assert response.status_code == 200