### 创建一个`SessionLocal`类

每个实例`SessionLocal`都会是一个数据库会话。当然该类本身还不是数据库会话。

但是一旦我们创建了一个`SessionLocal`类的实例，这个实例将是实际的数据库会话。

我们命名它是`SessionLocal`为了将它与我们从 SQLAlchemy 导入的`Session`区别开来。

稍后我们将使用`Session`（从 SQLAlchemy 导入的那个）。

要创建`SessionLocal`类，请使用函数`sessionmaker`：

```Python hl_lines="11"
{!../../../docs_src/sql_databases/sql_app/database.py!}
```

### 创建一个`Base`类

* API keys in:
    * Headers.
    * Các tham số trong query string.
    * Cookies, etc.

Cộng với tất cả các tính năng bảo mật từ Starlette (bao gồm **session cookies**).

Tất cả được xây dựng dưới dạng các công cụ và thành phần có thể tái sử dụng, dễ dàng tích hợp với hệ thống, kho lưu trữ dữ liệu, cơ sở dữ liệu quan hệ và NoSQL của bạn,...

### Dependency Injection

* Seriously impressive performance.
* WebSocket support.
* In-process background tasks.
* Startup and shutdown events.
* Test client built on HTTPX.
* CORS, GZip, Static Files, Streaming responses.
* Session and Cookie support.
* 100% test coverage.
* 100% type annotated codebase.
* Few hard dependencies.

### ✍ `SessionLocal` 🎓

🔠 👐 `SessionLocal` 🎓 🔜 💽 🎉. 🎓 ⚫️ 🚫 💽 🎉.

✋️ 🕐 👥 ✍ 👐 `SessionLocal` 🎓, 👉 👐 🔜 ☑ 💽 🎉.

👥 📛 ⚫️ `SessionLocal` 🔬 ⚫️ ⚪️➡️ `Session` 👥 🏭 ⚪️➡️ 🇸🇲.

👥 🔜 ⚙️ `Session` (1️⃣ 🗄 ⚪️➡️ 🇸🇲) ⏪.

✍ `SessionLocal` 🎓, ⚙️ 🔢 `sessionmaker`:

```Python hl_lines="11"
{!../../../docs_src/sql_databases/sql_app/database.py!}
```

### ✍ `Base` 🎓

* API Schlüssel in:
    * Header-Feldern.
    * Anfrageparametern.
    * Cookies, usw.

Zusätzlich alle Sicherheitsfunktionen von Starlette (inklusive **Session Cookies**).

Alles als wiederverwendbare Tools und Komponenten gebaut, die einfach in ihre Systeme, Datenspeicher, relationalen und nicht-relationalen Datenbanken, usw., integriert werden können.

    os.chdir(tmp_path)
    test_db = Path("./sql_app.db")
    if test_db.is_file():  # pragma: nocover
        test_db.unlink()
    # Import while creating the client to create the DB after starting the test session
    from docs_src.sql_databases.sql_app import main

    # Ensure import side effects are re-executed
    importlib.reload(main)
    with TestClient(main.app) as c:
        yield c

    os.chdir(tmp_path)
    test_db = Path("./sql_app.db")
    if test_db.is_file():  # pragma: nocover
        test_db.unlink()
    # Import while creating the client to create the DB after starting the test session
    from docs_src.sql_databases.sql_app_py310 import alt_main

    # Ensure import side effects are re-executed
    importlib.reload(alt_main)

    with TestClient(alt_main.app) as c:
        yield c

    opt raise
        dep -->> handler: Raise HTTPException
        handler -->> client: HTTP error response
        dep -->> dep: Raise other exception
    end
    dep ->> operation: Run dependency, e.g. DB session
    opt raise
        operation -->> handler: Raise HTTPException
        handler -->> client: HTTP error response
        operation -->> dep: Raise other exception
    end

* Suporte a **GraphQL**.
* Tarefas em processo _background_.
* Eventos na inicialização e encerramento.
* Cliente de testes construído sobre HTTPX.
* Respostas em **CORS**, GZip, Static Files, Streaming.
* Suporte a **Session e Cookie**.
* 100% de cobertura de testes.
* 100% do código utilizando _type annotations_.

## Recursos do Pydantic

* WebSocket-Unterstützung.
* Hintergrundtasks im selben Prozess.
* Events für das Hoch- und Herunterfahren.
* Testclient basierend auf HTTPX.
* CORS, GZip, statische Dateien, Streamende Responses.
* Session- und Cookie-Unterstützung.
* 100 % Testabdeckung.
* 100 % Typannotierte Codebasis.
* Wenige starke Abhängigkeiten.