# Testing a Database

!!! info
    These docs are about to be updated. 🎉

    The current version assumes Pydantic v1, and SQLAlchemy versions less than 2.0.

    The new docs will include Pydantic v2 and will use <a href="https://sqlmodel.tiangolo.com/" class="external-link" target="_blank">SQLModel</a> (which is also based on SQLAlchemy) once it is updated to use Pydantic v2 as well.

    ```

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.

You will have inline errors for the data that you send:

<img src="/img/tutorial/generate-clients/image04.png">

The response object will also have autocompletion:

<img src="/img/tutorial/generate-clients/image05.png">

## FastAPI App with Tags

In many cases your FastAPI app will be bigger, and you will probably use tags to separate different groups of *path operations*.

### Create an `Enum` class

Import `Enum` and create a sub-class that inherits from `str` and from `Enum`.

By inheriting from `str` the API docs will be able to know that the values must be of type `string` and will be able to render correctly.

Then create class attributes with fixed values, which will be the available valid values:

```Python hl_lines="1  6-9"
{!../../../docs_src/path_params/tutorial005.py!}
```

!!! info

<div class="termy">

```console
$ python -m venv env
```

</div>

That will create a directory `./env/` with the Python binaries, and then you will be able to install packages for that local environment.

### Activate the environment

Activate the new environment with:

=== "Linux, macOS"

    <div class="termy">

    If you have dependencies with `yield`, the exit code will run *after* the middleware.

    If there were any background tasks (documented later), they will run *after* all the middleware.

## Create a middleware

To create a middleware you use the decorator `@app.middleware("http")` on top of a function.

The middleware function receives:

* The `request`.
* A function `call_next` that will receive the `request` as a parameter.

```JSON
{
    "message": "Hello World",
    "root_path": "/api/v1"
}
```

So, it won't expect to be accessed at `http://127.0.0.1:8000/api/v1/app`.

## Add extra information

You can declare extra information in `Field`, `Query`, `Body`, etc. And it will be included in the generated JSON Schema.

You will learn more about adding extra information later in the docs, when learning to declare examples.

!!! warning
    Extra keys passed to `Field` will also be present in the resulting OpenAPI schema for your application.

If an incoming request does not validate correctly then a `400` response will be sent.

## `GZipMiddleware`

Handles GZip responses for any request that includes `"gzip"` in the `Accept-Encoding` header.

The middleware will handle both standard and streaming responses.

```Python hl_lines="2  6"
{!../../../docs_src/advanced_middleware/tutorial003.py!}
```

You will see the JSON response as:

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

### Interactive API docs

Now go to <a href="http://127.0.0.1:8000/docs" class="external-link" target="_blank">http://127.0.0.1:8000/docs</a>.