建立父-子文檔語法
首先看一下如何建立父子文檔，明顯和網上”_parent”的方式不一樣，說明es後期版本已經修改了語法
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PUT my_index
{
"mappings": {
"properties": {
"my_join_field": {
"type": "join",
"relations": {
"question": "answer"
}
}
}
}
}
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這段代碼建立了一個my_index的索引，其中my_join_field是一個用於join的字段，type爲join，關係relations爲：父爲question, 子爲answer
至於建立一父多子關係，只需要改爲數組即可："question": ["answer", "comment"]
插入數據
插入兩個父文檔，語法如下
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PUT my_index/_doc/1?refresh
{
"text": "This is a question",
"my_join_field": {
"name": "question"
}
}
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同時也可以省略name
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PUT my_index/_doc/1?refresh
{
"text": "This is a question",
"my_join_field": "question"
}
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插入子文檔
子文檔的插入語法如下，注意routing是父文檔的id，平時我們插入文檔時routing的默認就是id
此時name爲answer，表示這是個子文檔
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PUT /my_index/_doc/3?routing=1
{
"text": "This is an answer",
"my_join_field": {
"name": "answer",
"parent": "1"
}
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通過parent_id查詢子文檔
通過parent_id query傳入父文檔id即可
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GET my_index/_search
{
"query": {
"parent_id": {
"type": "answer",
"id": "1"
}
}
}
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父-子文檔的性能及限制性
父-子文檔主要適用於一對多的實體關係，將其反範式存入文檔中
父-子文檔主要由以下特性：
- Only one join field mapping is allowed per index.
每個索引只能有一個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-子文檔必須在同一個分片上，也就是說增刪改查一個子文檔，必須使用和父文檔一樣的routing key(默認是id) - An element can have multiple children but only one parent.
每個元素可以有多個子，但只有一個父 - It is possible to add a new relation to an existing join field.
可以爲一個已存在的join字段添加新的關聯關係 - It is also possible to add a child to an existing element but only if the element is already a parent.
可以在一個元素已經是父的情況下添加一個子
總結
es中通過父子文檔來實現join，但在一個索引中只能有一個一父多子的join
關係字段
es會自動生成一個額外的用於表示關係的字段：field#parent
我們可以通過以下方式查詢
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POST my_index/_search
{
"script_fields": {
"parent": {
"script": {
"source": "doc['my_join_field#question']"
}
}
}
}
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部分響應爲
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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"
]
}
}
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有_routing字段的說明是子文檔，它的parent字段是父文檔id，如果沒有_routing就是父文檔，它的parent指向當前id
全局序列
父-子文檔的join查詢使用一種叫做全局序列(Global ordinals)的技術來加速查詢，它採用預加載的方式構建，防止在第一次查詢或聚合時出現太長時間的延遲，但在索引元數據改變時重建，父文檔越多，構建時間就越長，重建在refresh時進行，這會造成refresh大量延遲時間(在refresh時也是預加載).
如果join字段很少用，可以關閉這種預加載模式:"eager_global_ordinals": false
全局序列的監控
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# 每個索引 curl -X GET "localhost:9200/_stats/fielddata?human&fields=my_join_field#question&pretty" # 每個節點上的每個索引 curl -X GET "localhost:9200/_nodes/stats/indices/fielddata?human&fields=my_join_field#question&pretty" |
一父多子的祖孫結構
考慮以下結構
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question
/ \
/ \
comment answer
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vote
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建立索引
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PUT my_index
{
"mappings": {
"properties": {
"my_join_field": {
"type": "join",
"relations": {
"question": ["answer", "comment"],
"answer": "vote"
}
}
}
}
}
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插入孫子節點
注意這裏的routing和parent值不一樣,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"
}
}
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has-child查詢
查詢包含特定子文檔的父文檔，這是一種很耗性能的查詢，儘量少用。它的查詢標準格式如下
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GET my_index/_search
{
"query": {
"has_child" : {
"type" : "child",
"query" : {
"match_all" : {}
},
"max_children": 10, //可選，符合查詢條件的子文檔最大返回數
"min_children": 2, //可選，符合查詢條件的子文檔最小返回數
"score_mode" : "min"
}
}
}
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測試代碼
部分測試代碼如下
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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"
}
}
# 通過parent_id查詢子文檔
GET my_index/_search
{
"query": {
"parent_id": {
"type": "answer",
"id": "8"
}
}
}
# 查詢relation
POST my_index/_search
{
"script_fields": {
"parent": {
"script": {
"source": "doc['my_join_field#question']"
}
}
}
}
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