# Unteranwendungen – Mounts

Wenn Sie zwei unabhängige FastAPI-Anwendungen mit deren eigenen unabhängigen OpenAPI und deren eigenen Dokumentationsoberflächen benötigen, können Sie eine Hauptanwendung haben und dann eine (oder mehrere) Unteranwendung(en) „mounten“.

## Mounten einer **FastAPI**-Anwendung

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/{item_id}")
async def read_item(item_id):

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        Union[str, None], Query(min_length=3, max_length=50, pattern="^fixedquery$")
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[Union[str, None], Query(alias="item-query")] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel, EmailStr

app = FastAPI()


class UserIn(BaseModel):
    username: str
    password: str
    email: EmailStr
    full_name: Union[str, None] = None


# Don't do this in production!
@app.post("/user/")
async def create_user(user: UserIn) -> UserIn:

from typing import Annotated

from fastapi import FastAPI, Path

app = FastAPI()


@app.get("/items/{item_id}")
async def read_items(
    item_id: Annotated[int, Path(title="The ID of the item to get", ge=1)], q: str
):
    results = {"item_id": item_id}
    if q:
        results.update({"q": q})

```JSON
{
    "message": "Hello World",
    "root_path": "/api/v1"
}
```

### ⚒ `root_path` FastAPI 📱

👐, 🚥 👆 🚫 ✔️ 🌌 🚚 📋 ⏸ 🎛 💖 `--root-path` ⚖️ 🌓, 👆 💪 ⚒ `root_path` 🔢 🕐❔ 🏗 👆 FastAPI 📱:

```Python hl_lines="3"
{!../../docs_src/behind_a_proxy/tutorial002.py!}
```

🚶‍♀️ `root_path` `FastAPI` 🔜 🌓 🚶‍♀️ `--root-path` 📋 ⏸ 🎛 Uvicorn ⚖️ Hypercorn.

### 🔃 `root_path`

from fastapi import FastAPI

app = FastAPI()


@app.get("/files/{file_path:path}")
async def read_file(file_path: str):

Dependencies are handled mainly with the special function `Depends()` that takes a callable.

Here is the reference for it and its parameters.

You can import it directly from `fastapi`:

```python
from fastapi import Depends
```

::: fastapi.Depends

## `Security()`

For many scenarios, you can handle security (authorization, authentication, etc.) with dependencies, using `Depends()`.

from fastapi import FastAPI

app = FastAPI()


@app.post("/index-weights/")
async def create_index_weights(weights: dict[int, float]):