etc.

                It will be used for:

                * Documentation: the generated OpenAPI (and the UI at `/docs`) will
                    show it as the response (JSON Schema).
                * Serialization: you could return an arbitrary object and the
                    `response_model` would be used to serialize that object into the

FastAPI will now:

* **Validate** the data making sure that the max length is 50 characters
* Show a **clear error** for the client when the data is not valid
* **Document** the parameter in the OpenAPI schema *path operation* (so it will show up in the **automatic docs UI**)

## Alternative (old) `Query` as the default value

You have been reading here some of the main concepts that you would probably need to keep in mind when deciding how to deploy your application:

* Security - HTTPS
* Running on startup
* Restarts
* Replication (the number of processes running)
* Memory
* Previous steps before starting

      "xaxis": {
        "mode": "time",
        "show": true,
        "values": []
      },
      "yaxes": [
        {
          "$$hashKey": "object:331",
          "format": "none",
          "logBase": 1,
          "show": true
        },
        {
          "$$hashKey": "object:332",
          "format": "short",
          "logBase": 1,
          "show": false
        }
      ],
      "yaxis": {

      "xaxis": {
        "mode": "time",
        "show": true,
        "values": []
      },
      "yaxes": [
        {
          "$$hashKey": "object:331",
          "format": "short",
          "logBase": 1,
          "show": true
        },
        {
          "$$hashKey": "object:332",
          "format": "short",
          "logBase": 1,
          "show": false
        }
      ],
      "yaxis": {

      "xaxis": {
        "mode": "time",
        "show": true,
        "values": []
      },
      "yaxes": [
        {
          "$$hashKey": "object:331",
          "format": "short",
          "logBase": 1,
          "show": true
        },
        {
          "$$hashKey": "object:332",
          "format": "short",
          "logBase": 1,
          "show": false
        }
      ],
      "yaxis": {

```Python hl_lines="3" title="app/routers/items.py"
{!../../../docs_src/bigger_applications/app/routers/items.py!}
```

#### How relative imports work

!!! tip
    If you know perfectly how imports work, continue to the next section below.

A single dot `.`, like in:

```Python
from .dependencies import get_token_header
```

would mean:

                documentation (by default at `/docs`).

                Read more about it in the
                [FastAPI docs about how to Configure Swagger UI](https://fastapi.tiangolo.com/how-to/configure-swagger-ui/).
                """
            ),
        ] = None,
        generate_unique_id_function: Annotated[
            Callable[[routing.APIRoute], str],

We just scratched the surface, but you already get the idea of how it all works.

Try changing the line with:

```Python
    return {"item_name": item.name, "item_id": item_id}
```

...from:

```Python
        ... "item_name": item.name ...
```

...to:

```Python
        ... "item_price": item.price ...
```

...and see how your editor will auto-complete the attributes and know their types:

#### Check the `openapi.json`

If you are curious about how the raw OpenAPI schema looks like, FastAPI automatically generates a JSON (schema) with the descriptions of all your API.

You can see it directly at: <a href="http://127.0.0.1:8000/openapi.json" class="external-link" target="_blank">http://127.0.0.1:8000/openapi.json</a>.

It will show a JSON starting with something like:

```JSON
{
    "openapi": "3.1.0",