The same way, you can define logic (code) that should be executed when the application is **shutting down**. In this case, this code will be executed **once**, **after** having handled possibly **many requests**.

```Python hl_lines="4  11  15-18"
{!../../../docs_src/templates/tutorial001.py!}
```

!!! note
    Before FastAPI 0.108.0, Starlette 0.29.0, the `name` was the first parameter.

    Also, before that, in previous versions, the `request` object was passed as part of the key-value pairs in the context for Jinja2.

!!! tip

```

## Create the database models

Let's now see the file `sql_app/models.py`.

### Create SQLAlchemy models from the `Base` class

We will use this `Base` class we created before to create the SQLAlchemy models.

!!! tip
    SQLAlchemy uses the term "**model**" to refer to these classes and instances that interact with the database.

## A database dependency with `yield`

For example, you could use this to create a database session and close it after finishing.

Only the code prior to and including the `yield` statement is executed before creating a response:

```Python hl_lines="2-4"
{!../../../docs_src/dependencies/tutorial007.py!}
```

The yielded value is what is injected into *path operations* and other dependencies:

```Python hl_lines="4"

    Make sure you [Upgrade the FastAPI version](../deployment/versions.md#upgrading-the-fastapi-versions){.internal-link target=_blank} to at least 0.95.1 before using `Annotated`.

## Declare metadata

You can declare all the same parameters as for `Query`.

For example, to declare a `title` metadata value for the path parameter `item_id` you can type:

=== "Python 3.10+"

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

    ```Python hl_lines="10"
    {!> ../../../docs_src/header_params/tutorial002.py!}
    ```

!!! warning
    Before setting `convert_underscores` to `False`, bear in mind that some HTTP proxies and servers disallow the usage of headers with underscores.

## Duplicate headers

You can also create an environment variable only for a specific program invocation, that is only available to that program, and only for its duration.

To do that, create it right before the program itself, on the same line:

<div class="termy">

```console
// Create an env var MY_NAME in line for this program call
$ MY_NAME="Wade Wilson" python main.py

# Separate OpenAPI Schemas for Input and Output or Not

When using **Pydantic v2**, the generated OpenAPI is a bit more exact and **correct** than before. 😎

In fact, in some cases, it will even have **two JSON Schemas** in OpenAPI for the same Pydantic model, for input and output, depending on if they have **default values**.

Let's see how that works and how to change it if you need to do that.

## Pydantic Models for Input and Output

You stand in line while several (let's say 8) cashiers that at the same time are cooks take the orders from the people in front of you.

Everyone before you is waiting for their burgers to be ready before leaving the counter because each of the 8 cashiers goes and prepares the burger right away before getting the next order.

<img src="/img/async/parallel-burgers/parallel-burgers-01.png" class="illustration">

[data-ty] {
    display: block;
    line-height: 2;
}

[data-ty]:before {
    /* Set up defaults and ensure empty lines are displayed. */
    content: '';
    display: inline-block;
    vertical-align: middle;
}

[data-ty="input"]:before,
[data-ty-prompt]:before {
    margin-right: 0.75em;
    color: var(--color-text-subtle);
}

[data-ty="input"]:before {
    content: '$';
}

[data-ty][data-ty-prompt]:before {