):
    response = await call_next(request)
    response.headers["custom"] = "foo"
    return response


@app.get("/user", dependencies=[Depends(set_up_request_state_dependency)])
def get_user():
    request_state = legacy_request_state_context_var.get()
    assert request_state
    return request_state["user"]


client = TestClient(app)


def test_dependency_contextvars():
    """

def read_users(skip: int = 0, limit: int = 100):
    users = crud.get_users(skip=skip, limit=limit)
    return users


@app.get(
    "/users/{user_id}", response_model=schemas.User, dependencies=[Depends(get_db)]
)
def read_user(user_id: int):
    db_user = crud.get_user(user_id=user_id)
    if db_user is None:
        raise HTTPException(status_code=404, detail="User not found")

from fastapi.testclient import TestClient

app = FastAPI()


user_router = APIRouter()
item_router = APIRouter()


@user_router.get("/")
def get_users():
    return [{"user_id": "u1"}, {"user_id": "u2"}]


@user_router.get("/{user_id}")
def get_user(user_id: str):
    return {"user_id": user_id}


@item_router.get("/")
def get_items(user_id: Optional[str] = None):
    if user_id is None:

{!> ../../docs_src/sql_databases/sql_app_py39/main.py!}
```

////

👥 🏗 💽 🎉 ⏭ 🔠 📨 🔗 ⏮️ `yield`, & ⤴️ 📪 ⚫️ ⏮️.

& ⤴️ 👥 💪 ✍ 🚚 🔗 *➡ 🛠️ 🔢*, 🤚 👈 🎉 🔗.

⏮️ 👈, 👥 💪 🤙 `crud.get_user` 🔗 ⚪️➡️ 🔘 *➡ 🛠️ 🔢* & ⚙️ 👈 🎉.

/// tip

👀 👈 💲 👆 📨 🇸🇲 🏷, ⚖️ 📇 🇸🇲 🏷.

{!> ../../docs_src/sql_databases/sql_app/main.py!}
```

////

我们在依赖项中的每个请求之前利用`yield`创建数据库会话，然后关闭它。

所以我们就可以在*路径操作函数*中创建需要的依赖，就能直接获取会话。

这样，我们就可以直接从*路径操作函数*内部调用`crud.get_user`并使用该会话，来进行对数据库操作。

/// tip

请注意，您返回的值是 SQLAlchemy 模型或 SQLAlchemy 模型列表。

但是由于所有路径操作的response_model都使用 Pydantic模型/使用orm_mode模式，因此您的 Pydantic 模型中声明的数据将从它们中提取并返回给客户端，并进行所有正常的过滤和验证。

///

/// tip

     *
     * @return A <code>String</code> containing the user for this message.
     */
    public String getUser() {
        return user;
    }

    /**
     * Sets the user for this message.
     *
     * @param user The user.
     */
    public void setUser(String user) {
        this.user = user;
    }

    /**

     * @param to
     * @param from
     */
    public static void cloneInternal ( Kerb5Authenticator to, Kerb5Authenticator from ) {
        NtlmPasswordAuthenticator.cloneInternal(to, from);
        to.setUser(from.getUser());
        to.setRealm(from.getRealm());
        to.setService(from.getService());
        to.setLifeTime(from.getLifeTime());
        to.setUserLifeTime(from.getUserLifeTime());

     *
     * @return A <code>String</code> containing the user for this message.
     */
    public String getUser () {
        return this.user;
    }


    /**
     * Sets the user for this message.
     *
     * @param user
     *            The user.
     */
    public void setUser ( String user ) {
        this.user = user;
    }


    /**

        registerModifiedProperty("searchWord");
        this.searchWord = value;
    }

    public String getUser() {
        checkSpecifiedProperty("user");
        return convertEmptyToNull(user);
    }

    public void setUser(String value) {
        registerModifiedProperty("user");
        this.user = value;
    }

    public String getUserAgent() {

		*GetUser("bulk_4", Config{Account: true, Pets: 3, Toys: 0, Company: false, Manager: true, Team: 0, Languages: 3, Friends: 0}),
		*GetUser("bulk_5", Config{Account: false, Pets: 0, Toys: 3, Company: true, Manager: false, Team: 1, Languages: 3, Friends: 1}),
		*GetUser("bulk_6", Config{Account: true, Pets: 4, Toys: 3, Company: false, Manager: true, Team: 1, Languages: 3, Friends: 0}),