# Children Aggregation 一种特殊的单桶聚合，可以将父文档类型上的桶聚合到子文档上。 此聚合依赖于映射中的[_parent](https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-parent-field.html)字段。 此聚合有一个选项： * type - 应该映射到父空间中的子类型的buckets(桶) 例如，假设我们有一个问题和答案的索引。 答案类型在映射中具有以下_parent字段 | `PUT child_example` `{` `"mappings": {` `"answer" : {` `"_parent" : {` `"type" : "question"` `}` `}` `}` `}` | 问题类型的文档包含标签字段，答案类型的文档包含所有者字段。 使用子集合，即使两个字段存在于两种不同类型的文档中，标记桶也可以在单个请求中映射到所有者桶。 一个问题类型文档的例子 | `PUT child_example/question/1` `{` `"body": "<p>I have Windows 2003 server and i bought a new Windows 2008 server...",` `"title": "Whats the best way to file transfer my site from server to a newer one?",` `"tags": [` `"windows-server-2003",` `"windows-server-2008",` `"file-transfer"` `]` `}` | 回答类型文件的例子: | `PUT child_example/answer/1?parent=1&refresh` `{` `"owner": {` `"location": "Norfolk, United Kingdom",` `"display_name": "Sam",` `"id": 48` `},` `"body": "<p>Unfortunately you're pretty much limited to FTP...",` `"creation_date": "2009-05-04T13:45:37.030"` `}` `PUT child_example/answer/2?parent=1&refresh` `{` `"owner": {` `"location": "Norfolk, United Kingdom",` `"display_name": "Troll",` `"id": 49` `},` `"body": "<p>Use Linux...",` `"creation_date": "2009-05-05T13:45:37.030"` `}` | 可以构建将两者连接在一起的以下请求： | `POST child_example/_search?size=0` `{` `"aggs": {` `"top-tags": {` `"terms": {` `"field": "tags.keyword",` `"size": 10` `},` `"aggs": {` `"to-answers": {` `"children": {` `"type" : "answer"  ＃1` `},` `"aggs": {` `"top-names": {` `"terms": {` `"field": "owner.display_name.keyword",` `"size": 10` `}` `}` `}` `}` `}` `}` `}` `}` | ＃1 **type** 指向使用名称为**answer**的 type / mapping 以上示例返回顶级问题标签和每个标签的顶级答案所有者。 下面是可能的返回结果： | `{` `"timed_out": false,` `"took": 25,` `"_shards": { "total": 5, "successful": 5, "failed": 0 },` `"hits": { "total": 3, "max_score": 0.0, hits: [] },` `"aggregations": {` `"top-tags": {` `"doc_count_error_upper_bound": 0,` `"sum_other_doc_count": 0,` `"buckets": [` `{` `"key": "file-transfer",` `"doc_count": 1, ＃1` `"to-answers": {` `"doc_count": 2, ＃2` `"top-names": {` `"doc_count_error_upper_bound": 0,` `"sum_other_doc_count": 0,` `"buckets": [` `{` `"key": "Sam",` `"doc_count": 1` `},` `{` `"key": "Troll",` `"doc_count": 1` `}` `]` `}` `}` `},` `{` `"key": "windows-server-2003",` `"doc_count": 1, ＃3` `"to-answers": {` `"doc_count": 2, ＃4` `"top-names": {` `"doc_count_error_upper_bound": 0,` `"sum_other_doc_count": 0,` `"buckets": [` `{` `"key": "Sam",` `"doc_count": 1` `},` `{` `"key": "Troll",` `"doc_count": 1` `}` `]` `}` `}` `},` `{` `"key": "windows-server-2008",` `"doc_count": 1, ＃5` `"to-answers": {` `"doc_count": 2, ＃6` `"top-names": {` `"doc_count_error_upper_bound": 0,` `"sum_other_doc_count": 0,` `"buckets": [` `{` `"key": "Sam",` `"doc_count": 1` `},` `{` `"key": "Troll",` `"doc_count": 1` `}` `]` `}` `}` `}` `]` `}` `}` `}` | ＃1  带有file-transfer，windows-server-2003等标签问题文档数量 ＃3 ＃5 ＃2  带有`file-transfer`, `windows-server-2003等标签的与问题文档相关的答复文档的数量` ＃4 ＃6