Elasticsearch 嵌套類型nested

時間 2019-12-06

原文原文鏈接

1.背景介紹

咱們在使用Elasticsearch作搜索引擎的時候有可能會遇到跨domain查詢的場景，好比作一個學生課程管理系統，搜一個學生的名字，像知道該學生的選課狀況。數組

固然解決問題的方法有不少，我能夠搜學生，而後去db查找學生關聯的選課，就能夠查到全部的課程，有時候數據量不是很大，而且個人索引只有一個課程維度的時候，就須要使用嵌套類型來解決這類問題。本文使用es和kibina來操做實例，由於基於中文的實例，還使用到了ik分詞器，具體能夠參考：bash

Elasticsearch安裝和使用
app

Elasticsearch中IK分詞器的使用dom

2.對象類型

Elasticsearch支持對象類型的存儲，咱們能夠把一個對象數組存到某個document的字段內，好比一個課程做爲一個document，那麼這個課程能夠創建一個students字段，存儲該課程下的學生object數組。post

在Elasticsearch中，新建一個以下的class_test索引，其中student做爲一個object數組類型。性能

PUT /class_test
{
  "mappings":{
	"class_test": {
		"properties": {
			"id": {
				"type": "keyword"
			},
			"name": {
				"analyzer": "ik_max_word",
				"type": "text"
			},
			"type":{
			  "type":"keyword"
			},
			"student":{
			    "properties": {
			       "name":{
			         "analyzer": "ik_max_word",
				        "type": "text"
			       },
			       "id":{
			         "type":"keyword"
			       }
			   }
		  }
      }
	  }
  },
  "settings":{
            "index": {
                "refresh_interval": "1s",
                "number_of_shards": 5,
                "max_result_window": "10000000",
                "mapper": {
                    "dynamic": "false"
                },
                "number_of_replicas": 0
            }
  }
}複製代碼

往class_test放入一下數據，如今索引裏面一共有兩條數據測試

{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 2,
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "class_test",
        "_type" : "class_test",
        "_id" : "ijfJ5GoBJeNZPNCWykLR",
        "_score" : 1.0,
        "_source" : {
          "id" : "1",
          "name" : "數學課",
          "student" : [
            {
              "id" : "1",
              "name" : "張三"
            },
            {
              "id" : "2",
              "name" : "李四"
            }
          ]
        }
      },
      {
        "_index" : "class_test",
        "_type" : "class_test",
        "_id" : "Q9NxGGsBa-TqHCWqAaM4",
        "_score" : 1.0,
        "_source" : {
          "id" : "2",
          "name" : "語文",
          "student" : [
            {
              "id" : "3",
              "name" : "傑克"
            },
            {
              "id" : "4",
              "name" : "瑪麗"
            }
          ]
        }
      }
    ]
  }
}複製代碼

接下來，咱們可使用查詢語句對索引進行查詢。當咱們查詢id爲1的學生參見的課程的時候，能夠查到數學課。搜索引擎

GET /class_test/class_test/_search
{
"query": {
  "bool": {
    "must": [
      {
        "match": {
          "student.id": "1"
        }
      }
    ]
  }
}
}複製代碼

{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 1,
    "max_score" : 0.2876821,
    "hits" : [
      {
        "_index" : "class_test",
        "_type" : "class_test",
        "_id" : "ijfJ5GoBJeNZPNCWykLR",
        "_score" : 0.2876821,
        "_source" : {
          "id" : "1",
          "name" : "數學課",
          "student" : [
            {
              "id" : "1",
              "name" : "張三"
            },
            {
              "id" : "2",
              "name" : "李四"
            }
          ]
        }
      }
    ]
  }
}
複製代碼

當咱們查名字叫張三的學生參加的課程的時候，也能查到數學課。spa

GET /class_test/class_test/_search
{
"query": {
  "bool": {
    "must": [
      {
        "match": {
          "student.name": "張三"
        }
      }
    ]
  }
}
}複製代碼

{
  "took" : 4,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 1,
    "max_score" : 0.5753642,
    "hits" : [
      {
        "_index" : "class_test",
        "_type" : "class_test",
        "_id" : "ijfJ5GoBJeNZPNCWykLR",
        "_score" : 0.5753642,
        "_source" : {
          "id" : "1",
          "name" : "數學課",
          "student" : [
            {
              "id" : "1",
              "name" : "張三"
            },
            {
              "id" : "2",
              "name" : "李四"
            }
          ]
        }
      }
    ]
  }
}複製代碼

可是當咱們查詢id爲1而且名字叫李四的學生參加的課程時code

GET /class_test/class_test/_search
{
"query": {
  "bool": {
    "must": [
      {
        "match": {
          "student.name": "李四"
        }
      },
      {
        "match": {
          "student.id": "1"
        }
        }
    ]
  }
}
}複製代碼

{
  "took" : 6,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 1,
    "max_score" : 0.8630463,
    "hits" : [
      {
        "_index" : "class_test",
        "_type" : "class_test",
        "_id" : "ijfJ5GoBJeNZPNCWykLR",
        "_score" : 0.8630463,
        "_source" : {
          "id" : "1",
          "name" : "數學課",
          "student" : [
            {
              "id" : "1",
              "name" : "張三"
            },
            {
              "id" : "2",
              "name" : "李四"
            }
          ]
        }
      }
    ]
  }
}
複製代碼

咱們發現，出來的結果也是數學課，這就有點奇怪，由於並無一個id爲1而且名字是李四的學生，那就不該該有這麼課。這是怎麼回事？原來在es內部，object數組類型會被打平，簡單來講咱們輸入的數組，實際存儲的類型是：

"student.id":[1,2],
"student.name":[張三,李四]複製代碼

因此倒排索引的創建，也是按照這種打平的邏輯。這個時候咱們能夠藉助Elasticsearch內的嵌套類型來解決問題。

3.Nested類型

和2中相似的，咱們須要建一個測試索引，名字爲class，不一樣的是student有了type字段，爲 "type":"nested"。

PUT /class
{
  "mappings":{
	"class": {
		"properties": {
			"id": {
				"type": "keyword"
			},
			"name": {
				"analyzer": "ik_max_word",
				"type": "text"
			},
			"type":{
			  "type":"keyword"
			},
			"student":{
			  "type":"nested",
			   "properties": {
			       "name":{
			         "analyzer": "ik_max_word",
				        "type": "text"
			       },
			       "id":{
			         "type":"keyword"
			       }
			   }
			  
			}
		}
	  }
  },
  "settings":{
            "index": {
                "refresh_interval": "1s",
                "number_of_shards": 5,
                "max_result_window": "10000000",
                "mapper": {
                    "dynamic": "false"
                },
                "number_of_replicas": 0
            }
  }
}複製代碼

咱們導入相同的數據，而後用搜索id爲1而且名字爲李四的學生的課程，這個時候咱們看到搜索結果爲空：

GET /class/class/_search
{
"query": {
  "bool": {
    "must": [
      {
        "nested": {
          "path": "student",
          "query": {
            "bool": {"must": [
              {
                "match": {
              "student.name": "李四"
                }
              },
              {
                "match": {
              "student.id": "1"
            }
              }
            ]}
          }
        }
      }
    ]
  }
}
}複製代碼

{
  "took" : 3,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 0,
    "max_score" : null,
    "hits" : [ ]
  }
}
複製代碼

4.其餘方式

其實解決這種跨domain的搜索還有一些其餘方式，對於嵌套類型，實際上是很是消耗Elasticsearch的性能的，咱們能夠選擇將須要搜索字段的值打平存一個字段，或者對學生單獨創建一個索引，而後去學生-班級映射關係表查詢班級。這一塊後面有機會再作介紹。

相關標籤/搜索

elasticsearch+elasticsearch

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