# Children Aggregation 一種特殊的單桶聚合，可以將父文檔類型上的桶聚合到子文檔上。 此聚合依賴于映射中的[_parent](https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-parent-field.html)字段。 此聚合有一個選項： * type -?應該映射到父空間中的子類型的buckets(桶) 例如，假設我們有一個問題和答案的索引。 答案類型在映射中具有以下_parent字段 | `PUT child_example` `{` `"mappings": {` `"answer" : {` `"_parent" : {` `"type" : "question"` `}` `}` `}` `}` | 問題類型的文檔包含標簽字段，答案類型的文檔包含所有者字段。 使用子集合，即使兩個字段存在于兩種不同類型的文檔中，標記桶也可以在單個請求中映射到所有者桶。 一個問題類型文檔的例子 | `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"` `]` `}` | 回答類型文件的例子: | `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"` `}` | 可以構建將兩者連接在一起的以下請求： | `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**?指向使用名稱為**answer**的?type / mapping 以上示例返回頂級問題標簽和每個標簽的頂級答案所有者。 下面是可能的返回結果： | `{` `"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 ?帶有file-transfer，windows-server-2003等標簽問題文檔數量 ＃3 ＃5 ＃2 ?帶有`file-transfer`,?`windows-server-2003等標簽的與問題文檔相關的答復文檔的數量` ＃4 ＃6