```console
$ fastapi dev main.py

<span style="color: green;">INFO</span>:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
```

</div>

Luego dirígete a la interfaz de `/docs`, verás que **FastAPI** está usando estos **modelos** para **documentar** la API, y los usará para **serializar** y **validar** los datos también.

<div class="screenshot">
<img src="/img/tutorial/sql-databases/image01.png">

func (s *ScanRange) Validate() error {
	if s == nil {
		return nil
	}
	if s.Start == nil && s.End == nil {
		// This parameter is optional, but when specified, it must not be empty.
		// Ref: https://docs.aws.amazon.com/AmazonS3/latest/API/API_SelectObjectContent.html#AmazonS3-SelectObjectContent-request-ScanRange
		return errors.New("ScanRange: No Start or End specified")
	}
	if s.Start == nil || s.End == nil {
		return nil

{* ../../docs_src/path_operation_advanced_configuration/tutorial005_py39.py hl[6] *}

If you open the automatic API docs, your extension will show up at the bottom of the specific *path operation*.

<img src="/img/tutorial/path-operation-advanced-configuration/image01.png">

   <span style="background-color:#007166"><font color="#D3D7CF"> server </font></span>  Documentation at <font color="#729FCF"><u style="text-decoration-style:solid">http://0.0.0.0:8000/docs</u></font>

             Logs:

     <span style="background-color:#007166"><font color="#D3D7CF"> INFO </font></span>  Started server process <b>[</b><font color="#34E2E2"><b>2306215</b></font><b>]</b>

	ARN string `xml:"CloudFunction"`
}

// Unused. Available for completion.
type topic struct {
	ARN string `xml:"Topic" json:"Topic"`
}

// Config - notification configuration described in
// http://docs.aws.amazon.com/AmazonS3/latest/dev/NotificationHowTo.html
type Config struct {
	XMLNS      string   `xml:"xmlns,attr,omitempty"`
	XMLName    xml.Name `xml:"NotificationConfiguration"`

type Status string

// Supported status types
const (
	Enabled  Status = "Enabled"
	Disabled Status = "Disabled"
)

// DeleteMarkerReplication - whether delete markers are replicated - https://docs.aws.amazon.com/AmazonS3/latest/dev/replication-add-config.html
type DeleteMarkerReplication struct {
	Status Status `xml:"Status"` // should be set to "Disabled" by default
}

   <span style="background-color:#007166"><font color="#D3D7CF"> server </font></span>  Documentation at <font color="#729FCF"><u style="text-decoration-style:solid">http://0.0.0.0:8000/docs</u></font>

             Logs:

     <span style="background-color:#007166"><font color="#D3D7CF"> INFO </font></span>  Started server process <b>[</b><font color="#34E2E2"><b>2306215</b></font><b>]</b>

Además de tipos singulares normales como `str`, `int`, `float`, etc., puedes usar tipos singulares más complejos que heredan de `str`.

Para ver todas las opciones que tienes, revisa el <a href="https://docs.pydantic.dev/latest/concepts/types/" class="external-link" target="_blank">Overview de Tipos de Pydantic</a>. Verás algunos ejemplos en el siguiente capítulo.

                    throwValidationError(messages -> messages.addErrorsCrudCouldNotFindCrudTable(GLOBAL, id), this::asListHtml);
                });
            });
        }).renderWith(data -> {
            data.register("docs", docList);
        });
    }

    // -----------------------------------------------------
    //                                         Actually Crud
    //                                         -------------

            <type>ActivationFile</type>
          </association>
        </field>
      </fields>
    </class>

    <!-- TODO: reproduced from maven-model/maven.mdo, instead should inherit code and link to external docs -->
    <class>
      <name>RepositoryBase</name>
      <version>1.0.0</version>
      <description><![CDATA[
         Repository contains the information needed