router_b = APIRouter(route_class=APIRouteB)
router_c = APIRouter(route_class=APIRouteC)


@router_a.get("/")
def get_a():
    return {"msg": "A"}


@router_b.get("/")
def get_b():
    return {"msg": "B"}


@router_c.get("/")
def get_c():
    return {"msg": "C"}


router_b.include_router(router=router_c, prefix="/c")
router_a.include_router(router=router_b, prefix="/b")

def get_a_b():
    return "Hello A B"


@router_a_b_override.get("/override", response_class=HTMLResponse)
def get_a_b_path_override():
    return "Hello A B"


@router_b_override.get("/")
def get_b():
    return "Hello B"


@router_b_override.get("/override", response_class=HTMLResponse)
def get_b_path_override():
    return "Hello B"


@router_b_a.get("/")
def get_b_a():
    return "Hello B A"

def get_a_b():
    return "Hello A B"


@router_a_b_override.get("/override", response_class=HTMLResponse)
def get_a_b_path_override():
    return "Hello A B"


@router_b_override.get("/")
def get_b():
    return "Hello B"


@router_b_override.get("/override", response_class=HTMLResponse)
def get_b_path_override():
    return "Hello B"


@router_b_a.get("/")
def get_b_a():
    return "Hello B A"

    database.db._state.reset()


def get_db(db_state=Depends(reset_db_state)):
    try:
        database.db.connect()
        yield
    finally:
        if not database.db.is_closed():
            database.db.close()


@app.post("/users/", response_model=schemas.User, dependencies=[Depends(get_db)])
def create_user(user: schemas.UserCreate):

async def get_db():
    db = DBSession()
    try:
        yield db
    finally:

    def __init__(self):
        self.db = DBSession()

    def __enter__(self):
        return self.db

    def __exit__(self, exc_type, exc_value, traceback):
        self.db.close()


async def get_db():
    with MySuperContextManager() as db:

Some requests will have a cached response. When this cached response isn’t fresh, OkHttp can do a _conditional GET_ to download an updated response if it’s newer than what’s cached. This requires headers like `If-Modified-Since` and `If-None-Match` to be added.

## Rewriting Responses

```

⤴️ 👥 🔜 📣 *➡ 🛠️ 🔢* & 🔗 🍵 `async def`, ⏮️ 😐 `def`,:

```Python hl_lines="2"
@app.get("/users/{user_id}", response_model=schemas.User)
def read_user(user_id: int, db: Session = Depends(get_db)):
    db_user = crud.get_user(db, user_id=user_id)
    ...
```

/// info

🚥 👆 💪 🔗 👆 🔗 💽 🔁, 👀 [🔁 🗄 (🔗) 💽](../advanced/async-sql-databases.md){.internal-link target=_blank}.

///

```

然后我们应该声明*路径操作函数*和不带 的依赖关系`async def`，只需使用普通的`def`，如下：

```Python hl_lines="2"
@app.get("/users/{user_id}", response_model=schemas.User)
def read_user(user_id: int, db: Session = Depends(get_db)):
    db_user = crud.get_user(db, user_id=user_id)
    ...
```

/// info

如果您需要异步连接到关系数据库，请参阅[Async SQL (Relational) Databases](https://fastapi.tiangolo.com/zh/advanced/async-sql-databases/)

///

* Make sure the `*` in short features in the docs is consistent (after `.`) in all languages. PR [#1424](https://github.com/tiangolo/fastapi/pull/1424).
* Update order of execution for `get_db` in SQLAlchemy tutorial. PR [#1293](https://github.com/tiangolo/fastapi/pull/1293) by [@bcb](https://github.com/bcb).
* Fix typos in Async docs. PR [#1423](https://github.com/tiangolo/fastapi/pull/1423).

## 0.54.2