## Use Case { #use-case }

Let's start with an example **use case** and then see how to solve it with this.

Let's imagine that you have some **machine learning models** that you want to use to handle requests. 🤖

/// info

Notice that we are only declaring one dependency in the *path operation function*, the `query_or_cookie_extractor`.

But **FastAPI** will know that it has to solve `query_extractor` first, to pass the results of that to `query_or_cookie_extractor` while calling it.

///

```mermaid
graph TB

query_extractor(["query_extractor"])

...it has the same parameters as our previous `common_parameters`:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8] *}

Those parameters are what **FastAPI** will use to "solve" the dependency.

In both cases, it will have:

* An optional `q` query parameter that is a `str`.
* A `skip` query parameter that is an `int`, with a default of `0`.

## Accessing the request body in an exception handler { #accessing-the-request-body-in-an-exception-handler }

/// tip

To solve this same problem, it's probably a lot easier to use the `body` in a custom handler for `RequestValidationError` ([Handling Errors](../tutorial/handling-errors.md#use-the-requestvalidationerror-body){.internal-link target=_blank}).

Now, as Swagger UI didn't support multiple JSON Schema examples (as of 2023-08-26), users didn't have a way to show multiple examples in the docs.

To solve that, FastAPI `0.103.0` **added support** for declaring the same old **OpenAPI-specific** `examples` field with the new parameter `openapi_examples`. 🤓

### Summary { #summary }

In discussions and PRs, in many cases, people bring their frustration and show it without filter, in many cases exaggerating, complaining, being entitled, etc. That's really not nice, and when it happens, it lowers our priority to solve their problems. But still, try to breath, and be gentle with your answers.

Try to avoid using bitter sarcasm or potentially passive-aggressive comments. If something is wrong, it's better to be direct (try to be gentle) than sarcastic.

        except Exception as e:
            http_error = HTTPException(
                status_code=400, detail="There was an error parsing the body"
            )
            raise http_error from e

        # Solve dependencies and run path operation function, auto-closing dependencies
        errors: list[Any] = []
        async_exit_stack = request.scope.get("fastapi_inner_astack")

            solved = await call(**solved_result.values)
        else:
            solved = await run_in_threadpool(call, **solved_result.values)
        if sub_dependant.name is not None:
            values[sub_dependant.name] = solved
        if sub_dependant.cache_key not in dependency_cache:
            dependency_cache[sub_dependant.cache_key] = solved
    path_values, path_errors = request_params_to_args(

    * This can solve nuanced errors when using middlewares. Before Starlette `0.24.0`, a new instance of each middleware class would be created when a new middleware was added. That normally was not a problem, unless the middleware class expected to be created only once, with only one instance, that happened in some cases. This upgrade would solve those cases (thanks [@adriangb](https://github.com/adriangb)! Starlette PR [#2017]...

You can combine normal FastAPI *path operations* with GraphQL on the same application.

/// tip

**GraphQL** solves some very specific use cases.

It has **advantages** and **disadvantages** when compared to common **web APIs**.

Make sure you evaluate if the **benefits** for your use case compensate the **drawbacks**. 🤓

///