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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(jí)字段，所有的字段用空格分開(kāi)，_all字段會(huì)被解析和索引，但是不存儲(chǔ)。當(dāng)你只想返回包含某個(gè)關(guān)鍵字的文檔但是不明確地搜某個(gè)字段的時(shí)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(lái)存儲(chǔ)文檔中的所有非空字段的名字，這個(gè)字段常用于exists查詢(xún)。例子如下:

terms查詢(xún)

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(jié)果會(huì)返回第二條文檔，因?yàn)榈谝粭l文檔沒(méi)有title字段。
同樣，可以使用exists查詢(xún)：

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(gè)_type和_id字段，_id可以用于term查詢(xún)、temrs查詢(xún)、match查詢(xún)、query_string查詢(xún)、simple_query_string查詢(xún)，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(xún)時(shí)，有時(shí)候只需要在特地索引名上進(jìn)行查詢(xún)，_index字段提供了便利，也就是說(shuō)可以對(duì)索引名進(jìn)行term查詢(xún)、terms查詢(xún)、聚合分析、使用腳本和排序。

_index是一個(gè)虛擬字段，不會(huì)真的加到Lucene索引中，對(duì)_index進(jìn)行term、terms查詢(xún)(也包括match、query_string、simple_query_string)，但是不支持prefix、wildcard、regexp和fuzzy查詢(xún)。

舉例，2個(gè)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(guān)系。下面例子中現(xiàn)在mapping中指定文檔的父子關(guān)系，然后索引父文檔，索引子文檔時(shí)指定父id，最后根據(jù)子文檔查詢(xún)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(guò)以下公式計(jì)算文檔應(yīng)該分到哪個(gè)分片上：

shard_num = hash(_routing) % num_primary_shards

默認(rèn)的_routing值是文檔的_id或者_(dá)parent，通過(guò)_routing參數(shù)可以設(shè)置自定義路由。例如，想把user1發(fā)布的博客存儲(chǔ)到同一個(gè)分片上，索引時(shí)指定routing參數(shù)，查詢(xún)時(shí)在指定路由上查詢(xún)：

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(chǔ)的文檔的原始值。默認(rèn)_source字段是開(kāi)啟的，也可以關(guān)閉：

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

但是一般情況下不要關(guān)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(jí)索引
• 通過(guò)原始字段debug查詢(xún)或者聚合

2.8 _type

每條被索引的文檔都有一個(gè)_type和_id字段，可以根據(jù)_type進(jìn)行查詢(xún)、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(xún)、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(zhuǎn)載于:https://my.oschina.net/LucasZhu/blog/1491778

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