**FastAPI** は`CommonQueryParams`クラスを呼び出します。これにより、そのクラスの「インスタンス」が作成され、インスタンスはパラメータ`commons`として関数に渡されます。

## 型注釈と`Depends`

上のコードでは`CommonQueryParams`を２回書いていることに注目してください:

```Python
commons: CommonQueryParams = Depends(CommonQueryParams)
```

以下にある最後の`CommonQueryParams`:

```Python
... = Depends(CommonQueryParams)
```

...は、**FastAPI** が依存関係を知るために実際に使用するものです。

Em algum momento, você provavelmente acabará escrevendo muitos programas diferentes que dependem de **pacotes diferentes**. E alguns desses projetos em que você trabalha dependerão de **versões diferentes** do mesmo pacote. 😱

Por exemplo, você pode criar um projeto chamado `philosophers-stone`, este programa depende de outro pacote chamado **`harry`, usando a versão `1`**. Então, você precisa instalar `harry`.

```mermaid

from __future__ import annotations

from typing import Annotated

from fastapi import Depends, FastAPI, Request
from fastapi.testclient import TestClient

from .utils import needs_py310


class Dep:
    def __call__(self, request: Request):
        return "test"


@needs_py310
def test_stringified_annotations():
    app = FastAPI()

    client = TestClient(app)

    @app.get("/test/")

from fastapi import Depends, FastAPI

app = FastAPI()


fake_items_db = [{"item_name": "Foo"}, {"item_name": "Bar"}, {"item_name": "Baz"}]


class CommonQueryParams:
    def __init__(self, q: Union[str, None] = None, skip: int = 0, limit: int = 100):
        self.q = q
        self.skip = skip
        self.limit = limit


@app.get("/items/")
async def read_items(commons: CommonQueryParams = Depends()):
    response = {}

from typing import Annotated, Union

from fastapi import Depends, FastAPI

app = FastAPI()


fake_items_db = [{"item_name": "Foo"}, {"item_name": "Bar"}, {"item_name": "Baz"}]


class CommonQueryParams:
    def __init__(self, q: Union[str, None] = None, skip: int = 0, limit: int = 100):
        self.q = q
        self.skip = skip
        self.limit = limit


@app.get("/items/")

from typing import Annotated, Union

from fastapi import BackgroundTasks, Depends, FastAPI

app = FastAPI()


def write_log(message: str):
    with open("log.txt", mode="a") as log:
        log.write(message)


def get_query(background_tasks: BackgroundTasks, q: Union[str, None] = None):
    if q:
        message = f"found query: {q}\n"
        background_tasks.add_task(write_log, message)
    return q

from typing import Annotated

from fastapi import Depends, FastAPI, HTTPException

app = FastAPI()


class InternalError(Exception):
    pass


def get_username():
    try:
        yield "Rick"
    except InternalError:
        print("Oops, we didn't raise again, Britney 😱")


@app.get("/items/{item_id}")
def get_item(item_id: str, username: Annotated[str, Depends(get_username)]):
    if item_id == "portal-gun":

///

{* ../../docs_src/security/tutorial005.py hl[4,139,166] *}

/// info | 技术细节

`Security` 实际上是 `Depends` 的子类，而且只比 `Depends` 多一个参数。

但使用 `Security` 代替 `Depends`，**FastAPI** 可以声明安全作用域，并在内部使用这些作用域，同时，使用 OpenAPI 存档 API。

但实际上，从 `fastapi` 导入的 `Query`、`Path`、`Depends`、`Security` 等对象，只是返回特殊类的函数。

///

## 使用 `SecurityScopes`

修改依赖项 `get_current_user`。

这是上面的依赖项使用的依赖项。

from fastapi import Depends, FastAPI, Security
from fastapi.security import APIKeyQuery
from fastapi.testclient import TestClient
from pydantic import BaseModel

app = FastAPI()

api_key = APIKeyQuery(name="key", description="API Key Query")


class User(BaseModel):
    username: str


def get_current_user(oauth_header: str = Security(api_key)):
    user = User(username=oauth_header)
    return user


@app.get("/users/me")

from typing import Union

from fastapi import Depends, FastAPI
from fastapi.testclient import TestClient

app = FastAPI()


async def common_parameters(
    q: Union[str, None] = None, skip: int = 0, limit: int = 100
):
    return {"q": q, "skip": skip, "limit": limit}


@app.get("/items/")
async def read_items(commons: dict = Depends(common_parameters)):
    return {"message": "Hello Items!", "params": commons}