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

!!! tip
    If you were connecting to a different database (e.g. PostgreSQL), you would need to change the `DATABASE_URL`.

## Create the tables

In this case, we are creating the tables in the same Python file, but in production, you would probably want to create them with Alembic, integrated with migrations, etc.

Кроме того, HTTP-заголовки не чувствительны к регистру, поэтому вы можете объявить их в стандартном стиле Python (также известном как "snake_case").

Таким образом вы можете использовать `user_agent`, как обычно, в коде Python, вместо того, чтобы вводить заглавные буквы как `User_Agent` или что-то подобное.

大部分标准请求头用**连字符**分隔，即**减号**（`-`）。

但是 `user-agent` 这样的变量在 Python 中是无效的。

因此，默认情况下，`Header` 把参数名中的字符由下划线（`_`）改为连字符（`-`）来提取并存档请求头 。

同时，HTTP 的请求头不区分大小写，可以使用 Python 标准样式（即 **snake_case**）进行声明。

因此，可以像在 Python 代码中一样使用 `user_agent` ，无需把首字母大写为 `User_Agent` 等形式。

如需禁用下划线自动转换为连字符，可以把 `Header` 的 `convert_underscores` 参数设置为 `False`：

=== "Python 3.10+"

    ```Python hl_lines="10"

    {!> ../../../docs_src/query_params/tutorial002_py310.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="9"
    {!> ../../../docs_src/query_params/tutorial002.py!}
    ```

In this case, the function parameter `q` will be optional, and will be `None` by default.

!!! check

    {!> ../../../docs_src/extra_models/tutorial005.py!}
    ```

## Recap

Use multiple Pydantic models and inherit freely for each case.

Here I'm also highlighting contributions from sponsors.

In the next sections you will see other options, configurations, and additional features.

!!! tip
    The next sections are **not necessarily "advanced"**.

    And it's possible that for your use case, the solution is in one of them.

## Read the Tutorial first

You could still use most of the features in **FastAPI** with the knowledge from the main [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank}.

## What is "Dependency Injection"

**"Dependency Injection"** means, in programming, that there is a way for your code (in this case, your *path operation functions*) to declare things that it requires to work and use: "dependencies".

And then, that system (in this case **FastAPI**) will take care of doing whatever is needed to provide your code with those needed dependencies ("inject" the dependencies).

=== "Python 3.8+ non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="10"
    {!> ../../../docs_src/dependencies/tutorial011.py!}
    ```

In this case, this `__call__` is what **FastAPI** will use to check for additional parameters and sub-dependencies, and this is what will be called to pass a value to the parameter in your *path operation function* later.

## Parameterize the instance

The contents that you return from your *path operation function* will be put inside of that `Response`.

And if that `Response` has a JSON media type (`application/json`), like is the case with the `JSONResponse` and `UJSONResponse`, the data you return will be automatically converted (and filtered) with any Pydantic `response_model` that you declared in the *path operation decorator*.

!!! note