Let's refer to the file `sql_app/database.py`.

### Import the SQLAlchemy parts

```Python hl_lines="1-3"
{!../../../docs_src/sql_databases/sql_app/database.py!}
```

### Create a database URL for SQLAlchemy

```Python hl_lines="5-6"
{!../../../docs_src/sql_databases/sql_app/database.py!}
```

In this example, we are "connecting" to a SQLite database (opening a file with the SQLite database).

{!../../../docs_src/async_sql_databases/tutorial001.py!}
```

!!! tip
    Notice that all this code is pure SQLAlchemy Core.

    `databases` is not doing anything here yet.

## Import and set up `databases`

* Import `databases`.
* Create a `DATABASE_URL`.
* Create a `database` object.

```Python hl_lines="3  9  12"
{!../../../docs_src/async_sql_databases/tutorial001.py!}
```

!!! tip

`sql_app` 🔜 ✔️ 📄 📁:

* `sql_app/__init__.py`: 🛁 📁.

* `sql_app/database.py`:

```Python
{!../../../docs_src/sql_databases_peewee/sql_app/database.py!}
```

* `sql_app/models.py`:

```Python
{!../../../docs_src/sql_databases_peewee/sql_app/models.py!}
```

* `sql_app/schemas.py`:

```Python
{!../../../docs_src/sql_databases_peewee/sql_app/schemas.py!}
```

* `sql_app/crud.py`:

* 创建 `DATABASE_URL`
* 创建 `database`

```Python hl_lines="3  9  12"
{!../../../docs_src/async_sql_databases/tutorial001.py!}
```

!!! tip "提示"

    连接 PostgreSQL 等数据库时，需要修改 `DATABASE_URL`。

## 创建表

本例中，使用 Python 文件创建表，但在生产环境中，应使用集成迁移等功能的 Alembic 创建表。

本例在启动 **FastAPI** 应用前，直接执行这些操作。

* 创建 `engine`
* 使用 `metadata` 对象创建所有表

```Python hl_lines="25-28"

initial_fake_database = {"rick": "Rick Sanchez"}

fake_database = initial_fake_database.copy()

initial_state = {"except": False, "finally": False}

state = initial_state.copy()

app = FastAPI()


async def get_database():
    temp_database = fake_database.copy()
    try:
        yield temp_database
        fake_database.update(temp_database)
    except HTTPException:

    - 🧰 [SQLModel](https://sqlmodel.tiangolo.com) for the Python SQL database interactions (ORM).
    - 🔍 [Pydantic](https://docs.pydantic.dev), used by FastAPI, for the data validation and settings management.
    - 💾 [PostgreSQL](https://www.postgresql.org) as the SQL database.
- 🚀 [React](https://react.dev) for the frontend.

---> 100%
```

</div>

## 创建 SQLAlchemy 部件

让我们转到文件`sql_app/database.py`。

### 导入 SQLAlchemy 部件

```Python hl_lines="1-3"
{!../../../docs_src/sql_databases/sql_app/database.py!}
```

### 为 SQLAlchemy 定义数据库 URL地址

```Python hl_lines="5-6"
{!../../../docs_src/sql_databases/sql_app/database.py!}
```

在这个例子中，我们正在“连接”到一个 SQLite 数据库（用 SQLite 数据库打开一个文件）。

$ pip install sqlalchemy

---> 100%
```

</div>

## ✍ 🇸🇲 🍕

➡️ 🔗 📁 `sql_app/database.py`.

### 🗄 🇸🇲 🍕

```Python hl_lines="1-3"
{!../../../docs_src/sql_databases/sql_app/database.py!}
```

### ✍ 💽 📛 🇸🇲

```Python hl_lines="5-6"
{!../../../docs_src/sql_databases/sql_app/database.py!}
```

👉 🖼, 👥 "🔗" 🗄 💽 (📂 📁 ⏮️ 🗄 💽).

📁 🔜 🔎 🎏 📁 📁 `sql_app.db`.

	Username           string    `json:"username"` // default: user running minio
	Password           string    `json:"password"` // default: no password
	Database           string    `json:"database"` // default: same as user
	QueueDir           string    `json:"queueDir"`
	QueueLimit         uint64    `json:"queueLimit"`
	MaxOpenConnections int       `json:"maxOpenConnections"`
}

use internally only data that doesn't depend on the resources of dependencies with `yield`.

For example, instead of using the same database session, you would create a new database session inside of the background task, and you would obtain the objects from the database using this new session. And then instead of passing the object from the database as a parameter to the background task function, you would pass the ID of that object and then obtain the object again inside the background...