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二、Meta-Fields(元數(shù)據(jù))

2.1 _all

_all字段是把其它字段拼接在一起的超級字段，所有的字段用空格分開，_all字段會被解析和索引，但是不存儲。當你只想返回包含某個關鍵字的文檔但是不明確地搜某個字段的時候就需要使用_all字段。
例子：

GET http://192.168.20.46:9200/my_index/blog/1 {"title": "Master Java","content": "learn java","author": "Tom" }

_all字段包含:[ “Master”, “Java”, “l(fā)earn”, “Tom” ]? 搜索：

POST http://192.168.20.46:9200/my_index/_search?pretty {"query": {"match": {"_all": "Java"}} }

使用copy_to自定義_all字段：

PUT http://192.168.20.46:9200/my_index {"mappings": {"mytype": {"properties": {"title": {"type": "text","copy_to": "full_content" },"content": {"type": "text","copy_to": "full_content" },"full_content": {"type": "text"}}}} } POST http://192.168.20.46:9200/my_index/mytype/1 {"title": "Master Java","content": "learn Java" } POST http://192.168.20.46:9200/my_index/_search?pretty {"query": {"match": {"full_content": "java"}} }

2.2 _field_names

_field_names字段用來存儲文檔中的所有非空字段的名字，這個字段常用于exists查詢。例子如下:

terms查詢

POST http://192.168.20.46:9200/my_index/my_type/1 {"title": "This is a document" } POST http://192.168.20.46:9200/my_index/my_type/2 {"title": "This is another document","body": "This document has a body" }POST http://192.168.20.46:9200/my_index/_search {"query": {"terms": {"_field_names": [ "body" ] }} }

結果會返回第二條文檔，因為第一條文檔沒有title字段。
同樣，可以使用exists查詢：

POST http://192.168.20.46:9200/my_index/_search {"query": {"exists" : { "field" : "body" }} }

2.3 _id

每條被索引的文檔都有一個_type和_id字段，_id可以用于term查詢、temrs查詢、match查詢、query_string查詢、simple_query_string查詢，但是不能用于聚合、腳本和排序。例子如下：

POST http://192.168.20.46:9200/my_index/my_type/1 {"text": "Document with ID 1" }POST http://192.168.20.46:9200/my_index/my_type/2 {"text": "Document with ID 2" }POST http://192.168.20.46:9200/my_index/_search {"query": {"terms": {"_id": [ "1", "2" ] }} }

2.4 _index

多索引查詢時，有時候只需要在特地索引名上進行查詢，_index字段提供了便利，也就是說可以對索引名進行term查詢、terms查詢、聚合分析、使用腳本和排序。

_index是一個虛擬字段，不會真的加到Lucene索引中，對_index進行term、terms查詢(也包括match、query_string、simple_query_string)，但是不支持prefix、wildcard、regexp和fuzzy查詢。

舉例，2個索引2條文檔

http://192.168.20.46:9200/index_1/my_type/1 {"text": "Document in index 1" }http://192.168.20.46:9200/index_2/my_type/2 {"text": "Document in index 2" }POST http://192.168.20.46:9200/index_1,index_2/_search {"query": {"terms": {"_index": ["index_1", "index_2"] }},"aggs": {"indices": {"terms": {"field": "_index", "size": 10}}},"sort": [{"_index": { "order": "asc"}}],"script_fields": {"index_name": {"script": {"lang": "painless","inline": "doc['_index']" }}} } {"took": 1210,"timed_out": false,"_shards": {"total": 10,"successful": 10,"failed": 0},"hits": {"total": 3,"max_score": null,"hits": [{"_index": "index_1","_type": "my_type","_id": "2","_score": null,"fields": {"index_name": ["index_1"]},"sort": ["index_1"]},{"_index": "index_1","_type": "my_type","_id": "1","_score": null,"fields": {"index_name": ["index_1"]},"sort": ["index_1"]},{"_index": "index_2","_type": "my_type","_id": "2","_score": null,"fields": {"index_name": ["index_2"]},"sort": ["index_2"]}]},"aggregations": {"indices": {"doc_count_error_upper_bound": 0,"sum_other_doc_count": 0,"buckets": [{"key": "index_1","doc_count": 2},{"key": "index_2","doc_count": 1}]}} }

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2.5 _parent

_parent用于指定同一索引中文檔的父子關系。下面例子中現(xiàn)在mapping中指定文檔的父子關系，然后索引父文檔，索引子文檔時指定父id，最后根據(jù)子文檔查詢父文檔。

POST http://192.168.20.46:9200/my_index {"mappings":{"my_parent":{},"my_child":{"_parent":{"type":{"type":"my_parent"}}}} } POST http://192.168.20.46:9200/my_index/my_parent/1 {"text": "This is a parent document" }POST http://192.168.20.46:9200/my_index/my_child/2?parent=1 {"text": "This is a child document" }POST http://192.168.20.46:9200/my_index/my_child/3?parent=1&refresh=true {"text": "This is another child document" } POST http://192.168.20.46:9200/my_index/my_parent/_search {"query": {"has_child": { "type": "my_child","query": {"match": {"text": "child document"}}}} }

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2.6 _routing

路由參數(shù)，ELasticsearch通過以下公式計算文檔應該分到哪個分片上：

shard_num = hash(_routing) % num_primary_shards

默認的_routing值是文檔的_id或者_parent，通過_routing參數(shù)可以設置自定義路由。例如，想把user1發(fā)布的博客存儲到同一個分片上，索引時指定routing參數(shù)，查詢時在指定路由上查詢：

POST http://192.168.20.46:9200/my_index/my_type/1?routing=user1&refresh=true {"title": "This is a document" } GET http://192.168.20.46:9200/my_index/my_type/1?routing=user1 ==> {"_index": "my_index","_type": "my_type","_id": "1","_version": 2,"_routing": "user1","found": true,"_source": {"title": "This is a document"} } POST http://192.168.20.46:9200/my_index/_search {"query": {"terms": {"_routing": [ "user1" ] }} }==> {"took": 33,"timed_out": false,"_shards": {"total": 5,"successful": 5,"failed": 0},"hits": {"total": 1,"max_score": 0.2876821,"hits": [{"_index": "my_index","_type": "my_type","_id": "1","_score": 0.2876821,"_routing": "user1","_source": {"title": "This is a document"}}]} } POST http://192.168.20.46:9200/my_index/_search?routing=user1,user2 {"query": {"match": {"title": "document"}} }

在Mapping中指定routing為必須的：

PUT http://192.168.20.46:9200/my_index2 {"mappings": {"my_type": {"_routing": {"required": true }}} } POST http://192.168.20.46:9200/my_index2/my_type/1 {"text": "No routing value provided routing_missing_exception" }

2.7 _source

存儲的文檔的原始值。默認_source字段是開啟的，也可以關閉：

POST http://192.168.20.46:9200/tweets {"mappings": {"tweet": {"_source": {"enabled": false}}} }

但是一般情況下不要關閉，除法你不想做一些操作：

• 使用update、update_by_query、reindex
• 使用高亮
• 數(shù)據(jù)備份、改變mapping、升級索引
• 通過原始字段debug查詢或者聚合

2.8 _type

每條被索引的文檔都有一個_type和_id字段，可以根據(jù)_type進行查詢、聚合、腳本和排序。例子如下：

POST http://192.168.20.46:9200/my_index/type_1/1 {"text": "Document with type 1" } POST http://192.168.20.46:9200/my_index/type_2/2?refresh=true {"text": "Document with type 2" }POST http://192.168.20.46:9200/my_index/_search {"query": {"terms": {"_type": [ "type_1", "type_2" ] }},"aggs": {"types": {"terms": {"field": "_type", "size": 10}}},"sort": [{"_type": { "order": "desc"}}],"script_fields": {"type": {"script": {"lang": "painless","inline": "doc['_type']" }}} }

2.9 _uid

_uid和_type和_index的組合。和_type一樣，可用于查詢、聚合、腳本和排序。例子如下：

POST http://192.168.20.46:9200/my_index/my_type/1 {"text": "Document with ID 1" } POST http://192.168.20.46:9200/my_index/my_type/2?refresh=true {"text": "Document with ID 2" }POST http://192.168.20.46:9200/my_index/_search {"query": {"terms": {"_uid": [ "my_type#1", "my_type#2" ] }},"aggs": {"UIDs": {"terms": {"field": "_uid", "size": 10}}},"sort": [{"_uid": { "order": "desc"}}],"script_fields": {"UID": {"script": {"lang": "painless","inline": "doc['_uid']" }}} }

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轉載于:https://my.oschina.net/LucasZhu/blog/1491778

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