FastAPI will use this return type to:

* **Validate** the returned data.
    * If the data is invalid (e.g. you are missing a field), it means that *your* app code is broken, not returning what it should, and it will return a server error instead of returning incorrect data. This way you and your clients can be certain that they will receive the data and the data shape expected.
* Add a **JSON Schema** for the response, in the OpenAPI *path operation*.

Do you want to have an `id` and `email` and not have any `username` in your model? Sure. You can use these same tools.

Do you want to just have a `str`? Or just a `dict`? Or a database class model instance directly? It all works the same way.

You actually don't have users that log in to your application but robots, bots, or other systems, that have just an access token? Again, it all works the same.

**FastAPI** vous permet de déclarer des informations et des validateurs additionnels pour vos paramètres de requêtes.

Commençons avec cette application pour exemple :

```Python hl_lines="9"
{!../../../docs_src/query_params_str_validations/tutorial001.py!}
```

In the output, there's a line with something like:

```hl_lines="4"
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
```

That line shows the URL where your app is being served, in your local machine.

### Check it

Open your browser at <a href="http://127.0.0.1:8000" class="external-link" target="_blank">http://127.0.0.1:8000</a>.

You will see the JSON response as:

```JSON
{"message": "Hello World"}

All the app code is the same, you can go back to that chapter check how it was.

The only changes here are in the new testing file.

Your normal dependency `get_db()` would return a database session.

In the test, you could use a dependency override to return your *custom* database session instead of the one that would be used normally.

In this example we'll create a temporary database only for the tests.

## File structure

Having a proxy with a stripped path prefix, in this case, means that you could declare a path at `/app` in your code, but then, you add a layer on top (the proxy) that would put your **FastAPI** application under a path like `/api/v1`.

In this case, the original path `/app` would actually be served at `/api/v1/app`.

Even though all your code is written assuming there's just `/app`.

```Python hl_lines="6"

If you create a Python file that imports and uses FastAPI, and run it with the Python from your local environment, it will use your cloned local FastAPI source code.

And if you update that local FastAPI source code when you run that Python file again, it will use the fresh version of FastAPI you just edited.

That way, you don't have to "install" your local version to be able to test every change.

!!! note "Technical Details"

                        }
                    }
                }
            }
        }
    }
}
```

## Types de médias supplémentaires pour la réponse principale

Vous pouvez utiliser ce même paramètre `responses` pour ajouter différents types de médias pour la même réponse principale.

J'y ai ensuite contribué, pour le rendre entièrement compatible avec JSON Schema, pour supporter différentes manières de définir les déclarations de contraintes, et pour améliorer le support des éditeurs (vérifications de type, autocomplétion) sur la base des tests effectués dans plusieurs éditeurs.

# Déploiement

Le déploiement d'une application **FastAPI** est relativement simple.

## Que signifie le déploiement

**Déployer** une application signifie effectuer les étapes nécessaires pour la rendre **disponible pour les
utilisateurs**.

Pour une **API Web**, cela implique normalement de la placer sur une **machine distante**, avec un **programme serveur**