For example, when using GraphQL you normally perform all the actions using only `POST` operations.

///

### Step 4: define the **path operation function** { #step-4-define-the-path-operation-function }

This is our "**path operation function**":

* **path**: is `/`.
* **operation**: is `get`.
* **function**: is the function below the "decorator" (below `@app.get("/")`).

{* ../../docs_src/first_steps/tutorial001.py hl[7] *}

```

...eso es porque el generador del cliente usa el **operation ID** interno de OpenAPI para cada *path operation*.

OpenAPI requiere que cada operation ID sea único a través de todas las *path operations*, por lo que FastAPI usa el **nombre de la función**, el **path**, y el **método/operación HTTP** para generar ese operation ID, porque de esa manera puede asegurarse de que los operation IDs sean únicos.

{* ../../docs_src/openapi_callbacks/tutorial001.py hl[3,25] *}

### Crear la *path operation* del callback

Para crear la *path operation* del callback utiliza el mismo `APIRouter` que creaste anteriormente.

Debería verse como una *path operation* normal de FastAPI:

* Probablemente debería tener una declaración del body que debería recibir, por ejemplo `body: InvoiceEvent`.

It is just a function that can take all the same parameters that a *path operation function* can take:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8:9] *}

That's it.

**2 lines**.

And it has the same shape and structure that all your *path operation functions* have.

You can think of it as a *path operation function* without the "decorator" (without the `@app.get("/some-path")`).

    }

    /**
     * Add a pending operation
     *
     * @param operation operation to add
     */
    public void addPendingOperation(CommonServerMessageBlock operation) {
        pendingOperations.add(operation);
    }

    /**
     * Remove a pending operation
     *
     * @param operation operation to remove
     * @return true if operation was removed
     */

    /**
     * SAMR CloseHandle operation for closing an opened SAM handle.
     * This operation releases resources associated with the handle.
     */
    public static class SamrCloseHandle extends DcerpcMessage {

        @Override
        public int getOpnum() {
            return 0x01;
        }

        /** The return value of the operation */
        public int retval;

    /**
     * SAMR CloseHandle operation for closing an opened SAM handle.
     * This operation releases resources associated with the handle.
     */
    public static class SamrCloseHandle extends DcerpcMessage {

        @Override
        public int getOpnum() {
            return 0x01;
        }

        /** The return value of the operation */
        public int retval;

... das liegt daran, dass der Client-Generator für jede *Pfadoperation* die OpenAPI-interne **Operation-ID** verwendet.

OpenAPI erfordert, dass jede Operation-ID innerhalb aller *Pfadoperationen* eindeutig ist. Daher verwendet FastAPI den **Funktionsnamen**, den **Pfad** und die **HTTP-Methode/-Operation**, um diese Operation-ID zu generieren. Denn so kann sichergestellt werden, dass die Operation-IDs eindeutig sind.

{* ../../docs_src/openapi_callbacks/tutorial001.py hl[3,25] *}

### Create the callback *path operation* { #create-the-callback-path-operation }

To create the callback *path operation* use the same `APIRouter` you created above.

It should look just like a normal FastAPI *path operation*:

* It should probably have a declaration of the body it should receive, e.g. `body: InvoiceEvent`.

Similar a como puedes [agregar `dependencies` a los *path operation decorators*](dependencies-in-path-operation-decorators.md){.internal-link target=_blank}, puedes agregarlos a la aplicación de `FastAPI`.

En ese caso, se aplicarán a todas las *path operations* en la aplicación:

{* ../../docs_src/dependencies/tutorial012_an_py39.py hl[16] *}