```

## 覆盖依赖项

接下来，创建覆盖依赖项，并为应用添加覆盖内容。

```Python hl_lines="19-24  27"
{!../../../docs_src/sql_databases/sql_app/tests/test_sql_app.py!}
```

!!! tip "提示"

    `overrider_get_db()` 与 `get_db` 的代码几乎完全一样，只是 `overrider_get_db` 中使用测试数据库的 `TestingSessionLocal`。

## 测试应用

然后，就可以正常测试了。

```Python hl_lines="32-47"
{!../../../docs_src/sql_databases/sql_app/tests/test_sql_app.py!}
```

models.Base.metadata.create_all(bind=engine)

app = FastAPI()


# Dependency
def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


@app.post("/users/", response_model=schemas.User)
def create_user(user: schemas.UserCreate, db: Session = Depends(get_db)):
    db_user = crud.get_user_by_email(db, email=user.email)
    if db_user:

```

## 🔗 🔐

🔜 👥 ✍ 🔗 🔐 & 🚮 ⚫️ 🔐 👆 📱.

```Python hl_lines="19-24  27"
{!../../../docs_src/sql_databases/sql_app/tests/test_sql_app.py!}
```

!!! tip
    📟 `override_get_db()` 🌖 ⚫️❔ 🎏 `get_db()`, ✋️ `override_get_db()` 👥 ⚙️ `TestingSessionLocal` 🔬 💽 ↩️.

## 💯 📱

⤴️ 👥 💪 💯 📱 🛎.

```Python hl_lines="32-47"
{!../../../docs_src/sql_databases/sql_app/tests/test_sql_app.py!}
```

👈, 👥 💪 ✍ ➕1️⃣ `async` 🔗 `reset_db_state()` 👈 ⚙️ 🎧-🔗 `get_db()`. ⚫️ 🔜 ⚒ 💲 🔑 🔢 (⏮️ 🔢 `dict`) 👈 🔜 ⚙️ 💽 🇵🇸 🎂 📨. & ⤴️ 🔗 `get_db()` 🔜 🏪 ⚫️ 💽 🇵🇸 (🔗, 💵, ♒️).

```Python hl_lines="18-20"
{!../../../docs_src/sql_databases_peewee/sql_app/main.py!}
```

**⏭ 📨**, 👥 🔜 ⏲ 👈 🔑 🔢 🔄 `async` 🔗 `reset_db_state()` & ⤴️ ✍ 🆕 🔗 `get_db()` 🔗, 👈 🆕 📨 🔜 ✔️ 🚮 👍 💽 🇵🇸 (🔗, 💵, ♒️).

!!! tip

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

For that, we need to create another `async` dependency `reset_db_state()` that is used as a sub-dependency in `get_db()`. It will set the value for the context variable (with just a default `dict`) that will be used as the database state for the whole request. And then the dependency `get_db()` will store in it the database state (connection, transactions, etc).

```Python hl_lines="18-20"

    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:

```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

```

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/)

```

⤴️ 👥 🔜 📣 *➡ 🛠️ 🔢* & 🔗 🍵 `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}.