# 异步 SQL 关系型数据库

**FastAPI** 使用 <a href="https://github.com/encode/databases" class="external-link" target="_blank">`encode/databases`</a> 为连接数据库提供异步支持（`async` 与 `await`）。

`databases` 兼容以下数据库：

* PostgreSQL
* MySQL
* SQLite

本章示例使用 **SQLite**，它使用的是单文件，且 Python 内置集成了 SQLite，因此，可以直接复制并运行本章示例。

生产环境下，则要使用 **PostgreSQL** 等数据库服务器。

!!! tip "提示"

Later, for your production application, you might want to use a database server like **PostgreSQL**.

!!! tip
    You could adopt ideas from the section about SQLAlchemy ORM ([SQL (Relational) Databases](../tutorial/sql-databases.md){.internal-link target=_blank}), like using utility functions to perform operations in the database, independent of your **FastAPI** code.

Harsha Laxman <******@****.***> 1687432812 -0700

{!../../../docs_src/sql_databases/sql_app/tests/test_sql_app.py!}
```

!!! tip
    The code for `override_get_db()` is almost exactly the same as for `get_db()`, but in `override_get_db()` we use the `TestingSessionLocal` for the testing database instead.

## Test the app

Then we can just test the app as normally.

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

        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.tests import test_sql_app

    # Ensure import side effects are re-executed
    importlib.reload(test_sql_app)
    test_sql_app.test_create_user()
    if test_db.is_file():  # pragma: nocover
        test_db.unlink()

    - sponsors: ../en/data/sponsors.yml
  redirects:
    redirect_maps:
      deployment/deta.md: deployment/cloud.md
      advanced/sql-databases-peewee.md: how-to/sql-databases-peewee.md
      advanced/async-sql-databases.md: how-to/async-sql-encode-databases.md
      advanced/nosql-databases.md: how-to/nosql-databases-couchbase.md
      advanced/graphql.md: how-to/graphql.md

        test_db.unlink()
    # Import while creating the client to create the DB after starting the test session
    from docs_src.sql_databases.sql_app.tests import test_sql_app

    # Ensure import side effects are re-executed
    importlib.reload(test_sql_app)
    test_sql_app.test_create_user()
    if test_db.is_file():  # pragma: nocover
        test_db.unlink()

```

一般是在 `main.py` 中调用这行代码，但在 `main.py` 里，这行代码用于创建 `sql_app.db`，但是现在要为测试创建 `test.db`。

因此，要在测试代码中添加这行代码创建新的数据库文件。

```Python hl_lines="16"
{!../../../docs_src/sql_databases/sql_app/tests/test_sql_app.py!}
```

## 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"

    - 🧰 [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.

        test_db.unlink()
    # Import while creating the client to create the DB after starting the test session
    from docs_src.sql_databases.sql_app_py39.tests import test_sql_app

    # Ensure import side effects are re-executed
    importlib.reload(test_sql_app)
    test_sql_app.test_create_user()
    if test_db.is_file():  # pragma: nocover
        test_db.unlink()