/// tip

Some editors check for unused function parameters, and show them as errors.

Using these `dependencies` in the *path operation decorator* you can make sure they are executed while avoiding editor/tooling errors.

It might also help avoid confusion for new developers that see an unused parameter in your code and could think it's unnecessary.

///

/// info

import java.lang.annotation.Target;

/**
 * Marks a method as an event subscriber.
 *
 * <p>The type of event will be indicated by the method's first (and only) parameter, which cannot
 * be primitive. If this annotation is applied to methods with zero parameters, or more than one
 * parameter, the object containing the method will not be able to register for event delivery from
 * the {@link EventBus}.
 *

		getCfgVal := func(cfgParam string) string {
			// As parameters are already validated, we skip checking
			// if the config param was found.
			val, _, _ := s.ResolveConfigParam(config.IdentityOpenIDSubSys, cfgName, cfgParam, false)
			return val
		}

		// In the past, when only one openID provider was allowed, there
		// was no `enable` parameter - the configuration is turned off

   *       to construct the sample instances. In case of tie, the candidate constructors or
   *       factories are tried one after another until one can be used to construct sample
   *       instances.
   *   <li>For the constructor or static factory method used to construct instances, it's checked

It will have a *path operation* that will receive an `Invoice` body, and a query parameter `callback_url` that will contain the URL for the callback.

This part is pretty normal, most of the code is probably already familiar to you:

```Python hl_lines="9-13  36-53"
{!../../docs_src/openapi_callbacks/tutorial001.py!}
```

/// tip

////

In diesem Fall ist dieses `__call__` das, was **FastAPI** verwendet, um nach zusätzlichen Parametern und Unterabhängigkeiten zu suchen, und das ist es auch, was später aufgerufen wird, um einen Wert an den Parameter in Ihrer *Pfadoperation-Funktion* zu übergeben.

## Die Instanz parametrisieren

Und jetzt können wir `__init__` verwenden, um die Parameter der Instanz zu deklarieren, die wir zum `Parametrisieren` der Abhängigkeit verwenden können:

# Body – Felder

So wie Sie zusätzliche Validation und Metadaten in Parametern der **Pfadoperation-Funktion** mittels `Query`, `Path` und `Body` deklarieren, können Sie auch innerhalb von Pydantic-Modellen zusätzliche Validation und Metadaten deklarieren, mittels Pydantics `Field`.

## `Field` importieren

Importieren Sie es zuerst:

//// tab | Python 3.10+

```Python hl_lines="4"
{!> ../../docs_src/body_fields/tutorial001_an_py310.py!}
```

* `@app.get()`
* `@app.post()`
* `@app.put()`
* `@app.delete()`
* usw.

{* ../../docs_src/response_status_code/tutorial001.py hl[6] *}

/// note | "Hinweis"

Dieser Teil ist ziemlich normal, der größte Teil des Codes ist Ihnen wahrscheinlich bereits bekannt:

```Python hl_lines="9-13  36-53"
{!../../docs_src/openapi_callbacks/tutorial001.py!}
```

/// tip | "Tipp"

    * le <abbr title="JavaScript Object Notation">JSON</abbr>.
    * <abbr title="en anglais : path parameters">les paramètres du chemin</abbr>.
    * <abbr title="en anglais : query parameters">les paramètres de la requête</abbr>.
    * les cookies.
    * <abbr title="en anglais : headers">les en-têtes</abbr>.
    * <abbr title="en anglais : forms">les formulaires</abbr>.