ElasticSearch7.2 父子文档

建立父-子文档语法

首先看一下如何建立父子文档，明显和网上”_parent”的方式不一样，说明es后期版本已经修改了语法

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PUT my_index { "mappings": { "properties": { "my_join_field": { "type": "join", "relations": { "question": "answer" } } } } }

 

这段代码建立了一个my_index的索引，其中my_join_field是一个用于join的字段，type为join，关系relations为：父为question, 子为answer
至于建立一父多子关系，只需要改为数组即可："question": ["answer", "comment"]

插入数据

插入两个父文档，语法如下

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PUT my_index/_doc/1?refresh { "text": "This is a question", "my_join_field": { "name": "question" } }

 

同时也可以省略name

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PUT my_index/_doc/1?refresh { "text": "This is a question", "my_join_field": "question" }

 

插入子文档

子文档的插入语法如下，注意routing是父文档的id，平时我们插入文档时routing的默认就是id
此时name为answer，表示这是个子文档

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PUT /my_index/_doc/3?routing=1 { "text": "This is an answer", "my_join_field": { "name": "answer", "parent": "1" }

 

通过parent_id查询子文档

通过parent_id query传入父文档id即可

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GET my_index/_search { "query": { "parent_id": { "type": "answer", "id": "1" } } }

 

父-子文档的性能及限制性

父-子文档主要适用于一对多的实体关系，将其反范式存入文档中

父-子文档主要由以下特性：

• Only one join field mapping is allowed per index.
  每个索引只能有一个join字段
• Parent and child documents must be indexed on the same shard. This means that the same routing value needs to be provided when getting, deleting, or updating a child document.
  父-子文档必须在同一个分片上，也就是说增删改查一个子文档，必须使用和父文档一样的routing key(默认是id)
• An element can have multiple children but only one parent.
  每个元素可以有多个子，但只有一个父
• It is possible to add a new relation to an existing join field.
  可以为一个已存在的join字段添加新的关联关系
• It is also possible to add a child to an existing element but only if the element is already a parent.
  可以在一个元素已经是父的情况下添加一个子

总结

es中通过父子文档来实现join，但在一个索引中只能有一个一父多子的join

关系字段

es会自动生成一个额外的用于表示关系的字段：field#parent
我们可以通过以下方式查询

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POST my_index/_search { "script_fields": { "parent": { "script": { "source": "doc['my_join_field#question']" } } } }

 

部分响应为

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{ "_index" : "my_index", "_type" : "_doc", "_id" : "8", "_score" : 1.0, "fields" : { "parent" : [ "8" ] } }, { "_index" : "my_index", "_type" : "_doc", "_id" : "4", "_score" : 1.0, "_routing" : "10", "fields" : { "parent" : [ "10" ] } }

 

有_routing字段的说明是子文档，它的parent字段是父文档id，如果没有_routing就是父文档，它的parent指向当前id

全局序列

父-子文档的join查询使用一种叫做全局序列(Global ordinals)的技术来加速查询，它采用预加载的方式构建，防止在第一次查询或聚合时出现太长时间的延迟，但在索引元数据改变时重建，父文档越多，构建时间就越长，重建在refresh时进行，这会造成refresh大量延迟时间(在refresh时也是预加载).
如果join字段很少用，可以关闭这种预加载模式:"eager_global_ordinals": false

全局序列的监控

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# 每个索引 curl -X GET "localhost:9200/_stats/fielddata?human&fields=my_join_field#question&pretty" # 每个节点上的每个索引 curl -X GET "localhost:9200/_nodes/stats/indices/fielddata?human&fields=my_join_field#question&pretty"

一父多子的祖孙结构

考虑以下结构

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question / \ / \ comment answer | | vote

 

建立索引

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PUT my_index { "mappings": { "properties": { "my_join_field": { "type": "join", "relations": { "question": ["answer", "comment"], "answer": "vote" } } } } }

 

插入孙子节点

注意这里的routing和parent值不一样,routing指的是祖父字段，即question,而parent指的就是字面意思answer

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PUT my_index/_doc/3?routing=1&refresh { "text": "This is a vote", "my_join_field": { "name": "vote", "parent": "2" } }

 

has-child查询

查询包含特定子文档的父文档，这是一种很耗性能的查询，尽量少用。它的查询标准格式如下

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GET my_index/_search { "query": { "has_child" : { "type" : "child", "query" : { "match_all" : {} }, "max_children": 10, //可选，符合查询条件的子文档最大返回数 "min_children": 2, //可选，符合查询条件的子文档最小返回数 "score_mode" : "min" } } }

 

测试代码

部分测试代码如下

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DELETE my_index PUT /my_index?pretty { "mappings": { "properties": { "my_join_field": { "type": "join", "relations": { "question": "answer" } } } } } # 插入父 PUT /my_index/_doc/8?refresh&pretty { "text": "This is a question", "my_join_field": { "name": "question" } } PUT /my_index/_doc/10?refresh&pretty { "text": "This is a new question", "my_join_field": { "name": "question" } } PUT /my_index/_doc/12?refresh&pretty { "text": "This is a new question", "my_join_field": { "name": "question" } } # 插入子 PUT /my_index/_doc/3?routing=8&refresh&pretty { "text": "This is an answer", "my_join_field": { "name": "answer", "parent": "8" } } PUT /my_index/_doc/4?routing=10&refresh&pretty { "text": "This is another answer", "my_join_field": { "name": "answer", "parent": "10" } } # 通过parent_id查询子文档 GET my_index/_search { "query": { "parent_id": { "type": "answer", "id": "8" } } } # 查询relation POST my_index/_search { "script_fields": { "parent": { "script": { "source": "doc['my_join_field#question']" } } } }