```

And all of them can use `yield`.

In this case `dependency_c`, to execute its exit code, needs the value from `dependency_b` (here named `dep_b`) to still be available.

And, in turn, `dependency_b` needs the value from `dependency_a` (here named `dep_a`) to be available for its exit code.

=== "Python 3.9+"

    ```Python hl_lines="18-19  26-27"

We could do better.

We can declare a `UserBase` model that serves as a base for our other models. And then we can make subclasses of that model that inherit its attributes (type declarations, validation, etc).

All the data conversion, validation, documentation, etc. will still work as normally.

Each of those response `dict`s can have a key `model`, containing a Pydantic model, just like `response_model`.

**FastAPI** will take that model, generate its JSON Schema and include it in the correct place in OpenAPI.

For example, to declare another response with a status code `404` and a Pydantic model `Message`, you can write:

```Python hl_lines="18  22"

    ├── __init__.py
    ├── crud.py
    ├── database.py
    ├── main.py
    ├── models.py
    └── schemas.py
```

The file `__init__.py` is just an empty file, but it tells Python that `sql_app` with all its modules (Python files) is a package.

Now let's see what each file/module does.

## Install `SQLAlchemy`

First you need to install `SQLAlchemy`:

<div class="termy">

```console
$ pip install sqlalchemy

```Python
burgers = await get_burgers(2)
```

The key here is the `await`. It tells Python that it has to wait ⏸ for `get_burgers(2)` to finish doing its thing 🕙 before storing the results in `burgers`. With that, Python will know that it can go and do something else 🔀 ⏯ in the meanwhile (like receiving another request).

And the dependency function `get_current_active_user` can also declare sub-dependencies, not only with `Depends` but also with `Security`. Declaring its own sub-dependency function (`get_current_user`), and more scope requirements.

In this case, it requires the scope `me` (it could require more than one scope).

!!! note

For example, Google login uses OpenID Connect (which underneath uses OAuth2).

But Facebook login doesn't support OpenID Connect. It has its own flavor of OAuth2.

### OpenID (not "OpenID Connect")

There was also an "OpenID" specification. That tried to solve the same thing as **OpenID Connect**, but was not based on OAuth2.

!!! note
    If you use a response class with no media type, FastAPI will expect your response to have no content, so it will not document the response format in its generated OpenAPI docs.

## Use `ORJSONResponse`

All the container management systems (like Docker or Kubernetes) have these networking features integrated into them.

## Containers and Processes

A **container image** normally includes in its metadata the default program or command that should be run when the **container** is started and the parameters to be passed to that program. Very similar to what would be if it was in the command line.

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