interface Transformer {
        /**
         * Interpolate the value read from the xml document
         *
         * @param source    The source value
         * @param fieldName A description of the field being interpolated. The implementation may use this to
         *                  log stuff.
         * @return the interpolated value
         */
        String transform(String source, String fieldName);

그리고 이를 어트리뷰트의 타입으로 사용할 수 있습니다:

{* ../../docs_src/body_nested_models/tutorial004_py310.py hl[18] *}

이는 **FastAPI**가 다음과 유사한 본문을 기대한다는 것을 의미합니다:

```JSON
{
    "name": "Foo",
    "description": "The pretender",
    "price": 42.0,
    "tax": 3.2,
    "tags": ["rock", "metal", "bar"],
    "image": {
        "url": "http://example.com/baz.jpg",
        "name": "The Foo live"
    }
}
```

### 将子模型用作类型 { #use-the-submodel-as-a-type }

然后我们可以将其用作一个属性的类型：

{* ../../docs_src/body_nested_models/tutorial004_py310.py hl[18] *}

这意味着 **FastAPI** 将期望类似于以下内容的请求体：

```JSON
{
    "name": "Foo",
    "description": "The pretender",
    "price": 42.0,
    "tax": 3.2,
    "tags": ["rock", "metal", "bar"],
    "image": {
        "url": "http://example.com/baz.jpg",
        "name": "The Foo live"
    }
}
```

        setDescription_Count("description", opLambda);
    }

    public void setDescription_Count(String name, ConditionOptionCall<ValueCountAggregationBuilder> opLambda) {
        ValueCountAggregationBuilder builder = regCountA(name, "description");
        if (opLambda != null) {
            opLambda.callback(builder);
        }
    }

            final String content = getStringValue(doc, "content");
            final String description = getStringValue(doc, "content_description");
            String descText = StringUtil.isNotBlank(content) ? content : description;
            descText = sanitizeDocumentContent(stripHtmlTags(descText));
            if (descText != null && descText.length() > maxChars) {

      maintainer="MinIO Inc <******@****.***>" \
      version="${RELEASE}" \
      release="${RELEASE}" \
      summary="MinIO is a High Performance Object Storage, API compatible with Amazon S3 cloud storage service." \

      maintainer="MinIO Inc <******@****.***>" \
      version="${RELEASE}" \
      release="${RELEASE}" \
      summary="MinIO is a High Performance Object Storage, API compatible with Amazon S3 cloud storage service." \

Cela pourrait être seulement une ou deux lignes de code, comme :

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
httpx.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

## 存档回调 { #documenting-the-callback }

实际的回调代码高度依赖于您自己的 API 应用。

并且可能每个应用都各不相同。

回调代码可能只有一两行，比如：

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
httpx.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

但回调最重要的部分可能是，根据 API 要发送给回调请求体的数据等内容，确保您的 API 用户（外部开发者）正确地实现*外部 API*。

因此，我们下一步要做的就是添加代码，为从 API 接收回调的*外部 API*存档。

这部分文档在 `/docs` 下的 Swagger UI 中显示，并且会告诉外部开发者如何构建*外部 API*。

    #; columnNullObjectMap = map:{
    #    ; providerPackage = $$packageBase$$.nogen.cache
    #    ; isGearedToSpecify = true
    #    ; columnMap = map:{
    #        ; MEMBER_STATUS = map:{
    #            ; DESCRIPTION = CachedMemberStatus.get(this, "$$columnName$$", $$primaryKey$$)
    #        }
    #        ; MEMBER_SECURITY = map:{
    #            ; REMINDER_ANSWER = CachedMemberSecurity.get(this, "$$columnName$$", $$primaryKey$$)