# Ref: https://github.com/fastapi/fastapi/issues/14271
from fastapi import Depends, FastAPI
from fastapi.security import HTTPBearer
from fastapi.testclient import TestClient
from inline_snapshot import snapshot

app = FastAPI()

bearer_scheme = HTTPBearer()


@app.get("/", dependencies=[Depends(bearer_scheme)])
async def get_root():
    return {"message": "Hello, World!"}

然后，依赖项函数返回包含这些值的 `dict`。

### 导入 `Depends`

{* ../../docs_src/dependencies/tutorial001.py hl[3] *}

### 声明依赖项

与在*路径操作函数*参数中使用 `Body`、`Query` 的方式相同，声明依赖项需要使用 `Depends` 和一个新的参数：

{* ../../docs_src/dependencies/tutorial001.py hl[15,20] *}

虽然，在路径操作函数的参数中使用 `Depends` 的方式与 `Body`、`Query` 相同，但 `Depends` 的工作方式略有不同。

这里只能传给 Depends 一个参数。

且该参数必须是可调用对象，比如函数。

该函数接收的参数和*路径操作函数*的参数一样。

from typing import Optional

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

app = FastAPI()

api_key = APIKeyHeader(name="key", auto_error=False)


class User(BaseModel):
    username: str


def get_current_user(oauth_header: Optional[str] = Security(api_key)):
    if oauth_header is None:
        return None

from typing import Annotated, TypeVar

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

app = FastAPI()

T = TypeVar("T")

Dep = Annotated[T, Depends()]


class A:
    pass


class B:
    pass


@app.get("/a")
async def a(dep: Dep[A]):
    return {"cls": dep.__class__.__name__}


@app.get("/b")
async def b(dep: Dep[B]):
    return {"cls": dep.__class__.__name__}

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

app = FastAPI()


async def user_exists(user_id: int):
    return True


@app.get("/users/{user_id}", dependencies=[Depends(user_exists)])
async def read_users(user_id: int):
    pass


client = TestClient(app)


def test_read_users():
    response = client.get("/users/42")
    assert response.status_code == 200, response.text

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

app = FastAPI()

api_key = APIKeyHeader(name="key")


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

app = FastAPI()

api_key = APIKeyHeader(name="key", description="An API Key Header")


class User(BaseModel):
    username: str


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

В версии 0.121.0 FastAPI добавил поддержку `Depends(scope="function")` для зависимостей с `yield`.

При использовании `Depends(scope="function")` код после `yield` выполняется сразу после завершения *функции-обработчика пути*, до отправки ответа клиенту.

А при использовании `Depends(scope="request")` (значение по умолчанию) код после `yield` выполняется после отправки ответа.

`Security` ist tatsächlich eine Unterklasse von `Depends` und hat nur noch einen zusätzlichen Parameter, den wir später kennenlernen werden.

Durch die Verwendung von `Security` anstelle von `Depends` weiß **FastAPI** jedoch, dass es Sicherheits-Scopes deklarieren, intern verwenden und die API mit OpenAPI dokumentieren kann.

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

app = FastAPI()

oid = OpenIdConnect(openIdConnectUrl="/openid")


class User(BaseModel):
    username: str


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