active_user(["active_user"])
admin_user(["admin_user"])
paying_user(["paying_user"])

public["/items/public/"]
private["/items/private/"]
activate_user["/users/{user_id}/activate"]
pro_items["/items/pro/"]

current_user --> active_user
active_user --> admin_user
active_user --> paying_user

current_user --> public
active_user --> private
admin_user --> activate_user
paying_user --> pro_items
```

    * If you are comparing Uvicorn, compare it against Daphne, Hypercorn, uWSGI, etc. Application servers.
* **Starlette**:
    * Will have the next best performance, after Uvicorn. In fact, Starlette uses Uvicorn to run. So, it probably can only get "slower" than Uvicorn by having to execute more code.

!!! check
    The way this dependency system is designed allows us to have different dependencies (different "dependables") that all return a `User` model.

    We are not restricted to having only one dependency that can return that type of data.

## Other models

active_user(["active_user"])
admin_user(["admin_user"])
paying_user(["paying_user"])

public["/items/public/"]
private["/items/private/"]
activate_user["/users/{user_id}/activate"]
pro_items["/items/pro/"]

current_user --> active_user
active_user --> admin_user
active_user --> paying_user

current_user --> public
active_user --> private
admin_user --> activate_user
paying_user --> pro_items
```

active_user(["active_user"])
admin_user(["admin_user"])
paying_user(["paying_user"])

public["/items/public/"]
private["/items/private/"]
activate_user["/users/{user_id}/activate"]
pro_items["/items/pro/"]

current_user --> active_user
active_user --> admin_user
active_user --> paying_user

current_user --> public
active_user --> private
admin_user --> activate_user
paying_user --> pro_items
```

# Advanced Dependencies

## Parameterized dependencies

All the dependencies we have seen are a fixed function or class.

But there could be cases where you want to be able to set parameters on the dependency, without having to declare many different functions or classes.

Let's imagine that we want to have a dependency that checks if the query parameter `q` contains some fixed content.

But we want to be able to parameterize that fixed content.

All the same process that applied for path parameters also applies for query parameters:

* Editor support (obviously)
* Data <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr>
* Data validation
* Automatic documentation

## Defaults

As query parameters are not a fixed part of a path, they can be optional and can have default values.

For those cases, you can use the `jsonable_encoder` to convert your data before passing it to a response:

```Python hl_lines="6-7  21-22"
{!../../../docs_src/response_directly/tutorial001.py!}
```

!!! note "Technical Details"
    You could also use `from starlette.responses import JSONResponse`.

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**.

Because this code is executed before the application **starts** taking requests, and right after it **finishes** handling requests, it covers the whole application **lifespan** (the word "lifespan" will be important in a second 😉).

For example:

* 200: `status.HTTP_200_OK`
* 403: `status.HTTP_403_FORBIDDEN`
* etc.

It can be convenient to quickly access HTTP (and WebSocket) status codes in your app, using autocompletion for the name without having to remember the integer status codes by memory.

Read more about it in the [FastAPI docs about Response Status Code](https://fastapi.tiangolo.com/tutorial/response-status-code/).

## Example

```python