* </ul>
     *
     * @param relPath is the path of the requested model source relative to this model source POM.
     * @return related model source or <code>null</code> if no such model source.
     */
    ModelSource2 getRelatedSource(String relPath);

    /**
     * Returns location of the POM, never <code>null</code>.
     */
    URI getLocationURI();

And Pydantic's `Field` returns an instance of `FieldInfo` as well.

`Body` also returns objects of a subclass of `FieldInfo` directly. And there are others you will see later that are subclasses of the `Body` class.

Remember that when you import `Query`, `Path`, and others from `fastapi`, those are actually functions that return special classes.

///

/// tip

### Use cases: external service { #use-cases-external-service }

An example could be that you have an external authentication provider that you need to call.

You send it a token and it returns an authenticated user.

This provider might be charging you per request, and calling it might take some extra time than if you had a fixed mock user for tests.

     * @return an OptionalEntity containing the file configuration if found, empty otherwise
     */
    public OptionalEntity<FileConfig> getFileConfig(final String id) {
        return fileConfigBhv.selectByPK(id);
    }

    /**
     * Retrieves a file configuration by its name.
     * If multiple configurations exist with the same name, returns the first one
     * ordered by sort order.

     */
    private samr() {
        // Utility class
    }

    /**
     * Returns the RPC interface syntax UUID and version for SAMR protocol.
     *
     * @return The SAMR interface UUID string
     */
    public static String getSyntax() {
        return "12345778-1234-abcd-ef00-0123456789ac:1.0";
    }

    /** Account control bit flag: Account is disabled */

     */
    private samr() {
        // Utility class
    }

    /**
     * Returns the RPC interface syntax UUID and version for SAMR protocol.
     *
     * @return The SAMR interface UUID string
     */
    public static String getSyntax() {
        return "12345778-1234-abcd-ef00-0123456789ac:1.0";
    }

    /** Account control bit flag: Account is disabled */

        return new ExtractData(getTextInternal(in, mimeTypeHelper, extractorFactory));
    }

    /**
     * Returns a text from the input stream.
     *
     * @param in The input stream.
     * @param mimeTypeHelper The mime type helper.
     * @param extractorFactory The extractor factory.
     * @return A text.
     */

        }

        return reference;
    }

    private boolean isNoteworthyException(Throwable exception) {
        if (exception == null) {
            return false;
        } else if (exception instanceof Error) {
            return true;
        } else if (exception instanceof RuntimeException) {
            return false;
        } else {

		if err != nil {
			return nil, err
		}
		// Check if we have a response ready or a filler byte.
		switch b {
		case 0:
			return reader, nil
		case 1:
			errorText, err := io.ReadAll(reader)
			if err != nil {
				return nil, err
			}
			return nil, errors.New(string(errorText))
		case 32:
			continue
		default:
			return nil, fmt.Errorf("unexpected filler byte: %d", b)
		}

E quando a dependência for resolvida, o **FastAPI** chamará este `checker` como:

```Python
checker(q="somequery")
```

...e passar o que quer que isso retorne como valor da dependência em nossa *função de operação de rota* como o parâmetro `fixed_content_included`:

{* ../../docs_src/dependencies/tutorial011_an_py39.py hl[22] *}

/// tip | Dica