添加回调前，首先看下常规 API 应用是什么样子。

常规 API 应用包含接收 `Invoice` 请求体的*路径操作*，还有包含回调 URL 的查询参数 `callback_url`。

这部分代码很常规，您对绝大多数代码应该都比较熟悉了：

{* ../../docs_src/openapi_callbacks/tutorial001.py hl[10:14,37:54] *}

/// tip | 提示

`callback_url` 查询参数使用 Pydantic 的 <a href="https://pydantic-docs.helpmanual.io/usage/types/#urls" class="external-link" target="_blank">URL</a> 类型。

///

}
```

y esperaría un response de esa *API externa* con un JSON body como:

```JSON
{
    "ok": true
}
```

/// tip | Consejo

Observa cómo la URL del callback utilizada contiene la URL recibida como parámetro de query en `callback_url` (`https://www.external.org/events`) y también el `id` de la factura desde dentro del JSON body (`2expen51ve`).

///

  <artifactId>t08-a</artifactId>
  <packaging>jar</packaging>
  <version>1.0</version>
  <repositories>
    <repository>
      <id>central</id>
      <name>Fake Maven Central Repository</name>
      <url>file://dummy</url>
    </repository>
  </repositories>
  <dependencies>
    <dependency>
      <groupId>maven-test</groupId>
      <artifactId>t08-b</artifactId>
      <version>1.0</version>
      <type>jar</type>

Wenn Ihre Datei `main.py` heißt, führen Sie Ihre Anwendung so aus:

<div class="termy">

```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>

Öffnen Sie Ihren Browser unter <a href="http://127.0.0.1:8000" class="external-link" target="_blank">http://127.0.0.1:8000</a>.

Sie sehen eine einfache Seite wie:

pkg net/http/httputil, type BufferPool interface, Put([]uint8)
pkg net/http/httputil, type ReverseProxy struct, BufferPool BufferPool
pkg net/url, method (*Error) Temporary() bool
pkg net/url, method (*Error) Timeout() bool
pkg net/url, method (InvalidHostError) Error() string
pkg net/url, type InvalidHostError string
pkg os/exec, type ExitError struct, Stderr []uint8
pkg regexp, method (*Regexp) Copy() *Regexp

	export AWS_ACCESS_KEY_ID=minio
	export AWS_SECRET_ACCESS_KEY=minio123
	aws --endpoint-url http://localhost:"$start_port" s3api create-multipart-upload --bucket bucket --key obj-1 >upload-id.json
	uploadId=$(jq -r '.UploadId' upload-id.json)

	truncate -s 5MiB file-5mib
	for i in {1..2}; do
		aws --endpoint-url http://localhost:"$start_port" s3api upload-part \
			--upload-id "$uploadId" --bucket bucket --key obj-1 \

            "termsOfService": "http://example.com/terms/",
            "contact": {
                "name": "Deadpoolio the Amazing",
                "url": "http://x-force.example.com/contact/",
                "email": "******@****.***",
            },
            "license": {
                "name": "Apache 2.0",
                "identifier": "MIT",
            },

                    }
                },
                "summary": "Read Sub",
                "operationId": "read_sub_sub_get",
            }
        }
    },
    "servers": [{"url": "/subapi"}],
}


def test_openapi_schema_main():
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == openapi_schema_main

For example, as in the `Image` model we have a `url` field, we can declare it to be an instance of Pydantic's `HttpUrl` instead of a `str`:

{* ../../docs_src/body_nested_models/tutorial005_py310.py hl[2,8] *}

The string will be checked to be a valid URL, and documented in JSON Schema / OpenAPI as such.

Например, так как в модели `Image` у нас есть поле `url`, то мы можем объявить его как тип `HttpUrl` из Pydantic вместо типа `str`:

{* ../../docs_src/body_nested_models/tutorial005_py310.py hl[2,8] *}

Строка будет проверена на соответствие допустимому URL-адресу и задокументирована в JSON Schema / OpenAPI как таковая.