"responses": {
                        "200": {
                            "description": "Successful Response",
                            "content": {
                                "application/json": {
                                    "schema": {"$ref": "#/components/schemas/Item"}
                                }
                            },
                        },
                        "422": {

import org.apache.maven.api.annotations.Nullable;

/**
 * Represents a hierarchical trace of nested requests within a session, enabling correlation between
 * session events and their originating operations in the application code. The trace structure
 * supports the following key features:
 *
 * <ul>
 *   <li>Maintains parent-child relationships between requests to track operation nesting</li>

    You could have custom internal logic to separate it by colon characters (`:`) or
    similar, and get the two parts `items` and `read`. Many applications do that to
    group and organize permissions, you could do it as well in your application, just
    know that that it is application specific, it's not part of the specification.
    """

    def __init__(
        self,
        *,
        grant_type: Annotated[

                            "description": "Successful Response",
                            "content": {"application/json": {"schema": {}}},
                        },
                        "422": {
                            "description": "Validation Error",
                            "content": {
                                "application/json": {
                                    "schema": {

                            "description": "Successful Response",
                            "content": {"application/json": {"schema": {}}},
                        },
                        "422": {
                            "description": "Validation Error",
                            "content": {
                                "application/json": {
                                    "schema": {

You can add middleware to **FastAPI** applications.

A "middleware" is a function that works with every **request** before it is processed by any specific *path operation*. And also with every **response** before returning it.

* It takes each **request** that comes to your application.
* It can then do something to that **request** or run any needed code.
* Then it passes the **request** to be processed by the rest of the application (by some *path operation*).

                            "content": {
                                "application/json": {
                                    "schema": {},
                                }
                            },
                        },
                        "422": {
                            "content": {
                                "application/json": {
                                    "schema": {

                            "description": "Return the JSON item or an image.",
                            "content": {
                                "image/png": {},
                                "application/json": {
                                    "schema": {"$ref": "#/components/schemas/Item"}
                                },
                            },
                        },
                        "422": {

                            "description": "Successful Response",
                            "content": {"application/json": {"schema": {}}},
                        },
                        "422": {
                            "description": "Validation Error",
                            "content": {
                                "application/json": {
                                    "schema": {

Puedes declarar múltiples parámetros `Form` en una *path operation*, pero no puedes también declarar campos `Body` que esperas recibir como JSON, ya que el request tendrá el body codificado usando `application/x-www-form-urlencoded` en lugar de `application/json`.

Esto no es una limitación de **FastAPI**, es parte del protocolo HTTP.

///

## Recapitulación { #recap }