## 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. 🤖

That's why in this example we have to declare it in the `response_model` parameter.

...but continue reading below to see how to overcome that.

## Return Type and Data Filtering { #return-type-and-data-filtering }

        + "]}";
  }

  public static void main(String[] args) throws IOException {
    PostExample example = new PostExample();
    String json = example.bowlingJson("Jesse", "Jake");
    String response = example.post("http://www.roundsapp.com/post", json);
    System.out.println(response);
  }

        responseData.setUrl("http://example.com/");
        responseData.setMimeType("text/html");
        return responseData;
    }

    private ResponseData getTestData2() {
        final ResponseData responseData = new ResponseData();
        responseData.setHttpStatusCode(200);
        responseData.setUrl("https://example.com/");
        responseData.setMimeType("text/html");

**FastAPI** will keep the additional information from `responses`, and combine it with the JSON Schema from your model.

For example, you can declare a response with a status code `404` that uses a Pydantic model and has a custom `description`.

And a response with a status code `200` that uses your `response_model`, but includes a custom `example`:

{* ../../docs_src/additional_responses/tutorial003_py39.py hl[20:31] *}

def get_settings_override():
    return Settings(admin_email="testing_admin@example.com")


app.dependency_overrides[get_settings] = get_settings_override


def test_app():
    response = client.get("/info")
    data = response.json()
    assert data == {
        "app_name": "Awesome API",
        "admin_email": "testing_admin@example.com",
        "items_per_user": 50,

 *
 * @since 4.0.0
 */
@Experimental
public interface VersionParser extends Service {

    /**
     * Parses the specified version string, for example "1.0".
     *
     * @param version the version string to parse, must not be {@code null}
     * @return the parsed version, never {@code null}

 *
 * <p>Example usage:</p>
 * <pre>
 * {@code
 * XPathAPI xPathAPI = new XPathAPI();
 * NodeList nodes = xPathAPI.selectNodeList(contextNode, "//example");
 * Node singleNode = xPathAPI.selectSingleNode(contextNode, "//example[1]");
 * XPathEvaluationResult<?> result = xPathAPI.eval(contextNode, "count(//example)");
 * }
 * </pre>
 *

# Query Parameters and String Validations { #query-parameters-and-string-validations }

**FastAPI** allows you to declare additional information and validation for your parameters.

Let's take this application as example:

{* ../../docs_src/query_params_str_validations/tutorial001_py310.py hl[7] *}

fake_users_db = {
    "johndoe": {
        "username": "johndoe",
        "full_name": "John Doe",
        "email": "johndoe@example.com",
        "hashed_password": "fakehashedsecret",
        "disabled": False,
    },
    "alice": {
        "username": "alice",
        "full_name": "Alice Wonderson",
        "email": "alice@example.com",
        "hashed_password": "fakehashedsecret2",
        "disabled": True,
    },
}

app = FastAPI()