### 歡迎訪問我的GitHub
> 這裡分類和彙總了欣宸的全部原創(含配套原始碼)：[https://github.com/zq2599/blog_demos](https://github.com/zq2599/blog_demos)

### 本篇概覽
- 《Elasticsearch實戰》(英文名Elasticsearch IN ACTION)是經典es教程，對應demo原始碼地址為：https://github.com/dakrone/elasticsearch-in-action ，最新分支**6.x**，在使用原始碼時，發現索引_doc的靜態對映指令碼增加了一個型別為**join**的欄位，如下所示，：

```shell
"mappings" : {
    "_doc" : {
      "_source" : {
        "enabled" : true
      },
      "properties" : {
        "relationship_type": {
          "type": "join",
          "relations" : {
            "group": "event"
          }
        },
        ...
```
- 這是es6新增的型別，一起來透過實戰學習這個join；

### 環境資訊
1. 作業系統：Ubuntu 18.04.2 LTS
2. elasticsearch：6.7.1
3. kibana：6.7.1

### 《Elasticsearch實戰》demo原始碼下載地址
- 本文用到的原始碼一共兩個檔案，一個是建立靜態對映的mapping.json， 另一個是建立文件的populate.sh ， 地址分別如下：

1. https://github.com/dakrone/elasticsearch-in-action/blob/6.x/mapping.json
2. https://github.com/dakrone/elasticsearch-in-action/blob/6.x/populate.sh

- 上述檔案的用法：下載到同一個目錄，執行命令**./populate.sh 192.168.1.101:9200** ，"192.168.1.101:9200"是es6的http地址和埠；
### 官方說法
- 官方對join型別的說明如下：
![在這裡插入圖片描述](https://img-blog.csdnimg.cn/20190407134929508.jpg?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly94aW5jaGVuLmJsb2cuY3Nkbi5uZXQ=,size_16,color_FFFFFF,t_70)

- 我的理解：
1. join型別用於建立索引內文件的父子關係；
2. 用父子文件的名字來表示關係；

- 接下來看看《Elasticsearch實戰》的demo中是怎麼使用這個欄位的；

### 《Elasticsearch實戰》的demo
- demo中部分文件的建立指令碼如下所示：

```shell
curl -s -XPOST "$ADDRESS/get-together/_doc/1" -H'Content-Type: application/json' -d'{
  "relationship_type": "group",
  "name": "Denver Clojure",
  "organizer": ["Daniel", "Lee"],
  "description": "Group of Clojure enthusiasts from Denver who want to hack on code together and learn more about Clojure",
  "created_on": "2012-06-15",
  "tags": ["clojure", "denver", "functional programming", "jvm", "java"],
  "members": ["Lee", "Daniel", "Mike"],
  "location_group": "Denver, Colorado, USA"
}'

curl -s -XPOST "$ADDRESS/get-together/_doc/100?routing=1" -H'Content-Type: application/json' -d'{
  "relationship_type": {
    "name": "event",
    "parent": "1"
  },
  "host": ["Lee", "Troy"],
  "title": "Liberator and Immutant",
  "description": "We will discuss two different frameworks in Clojure for doing different things. Liberator is a ring-compatible web framework based on Erlang Webmachine. Immutant is an all-in-one enterprise application based on JBoss.",
  "attendees": ["Lee", "Troy", "Daniel", "Tom"],
  "date": "2013-09-05T18:00",
  "location_event": {
    "name": "Stoneys Full Steam Tavern",
    "geolocation": "39.752337,-105.00083"
  },
  "reviews": 4
}'
```

- 如上所示，id為1的記錄，其relationship_type欄位的值為"group"，id為2的記錄，relationship_type欄位的值不是字串，而是物件，parent為1表示父文件id為1，name為"event"表示父子關係是"group:event"型別；

- **注意：上述第二個文件的地址中攜帶了routing引數，以保持父子在同一個分片，這是在使用join型別是要格外注意的地方；**

- 接下來，確保前面提到的populate.sh指令碼已經執行，使得_doc索引及其文件資料在es環境中準備好，就可以實戰了，實戰環境是Kibana的Det Tools：

### 查詢所有父型別為"group"的文件(結果是子文件)：
- 執行如下指令碼：

```shell
GET get-together/_search
{
  "query": {
    "has_parent": {
      "parent_type": "group",
      "query": {
        "match_all": {}
      }
    }
  }
}
```

- 可以得到所有父型別為"group"的子文件：

```shell
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 2,
    "successful" : 2,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 15,
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "get-together",
        "_type" : "_doc",
        "_id" : "106",
        "_score" : 1.0,
        "_routing" : "3",
        "_source" : {
          "relationship_type" : {
            "name" : "event",
            "parent" : "3"
          },
          "host" : "Mik",
          "title" : "Social management and monitoring tools",
          "description" : "Shay Banon will be there to answer questions and we can talk about management tools.",
          "attendees" : [
            "Shay",
            "Mik",
            "John",
            "Chris"
          ],
          "date" : "2013-03-06T18:00",
          "location_event" : {
            "name" : "Quid Inc",
            "geolocation" : "37.798442,-122.399801"
          },
          "reviews" : 5
        }
      },
      {
        "_index" : "get-together",
        "_type" : "_doc",
        "_id" : "107",
        "_score" : 1.0,
        "_routing" : "3",
        "_source" : {
          "relationship_type" : {
            "name" : "event",
            "parent" : "3"
          },
          "host" : "Mik",
          "title" : "Logging and Elasticsearch",
          "description" : "Get a deep dive for what Elasticsearch is and how it can be used for logging with Logstash as well as Kibana!",
          "attendees" : [
            "Shay",
            "Rashid",
            "Erik",
            "Grant",
            "Mik"
          ],
          "date" : "2013-04-08T18:00",
          "location_event" : {
            "name" : "Salesforce headquarters",
            "geolocation" : "37.793592,-122.397033"
          },
          "reviews" : 3
        }
      },
     ...
```

### 查詢所有子型別為"event"的文件（結果是父文件）

- 執行如下指令碼：

```shell
GET get-together/_search
{
  "query": {
    "has_child": {
      "type": "event",
      "query": {
        "match_all": {}
      }
    }
  }
}
```

- 可以得到所有子型別為"event"的文件：

```shell
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 2,
    "successful" : 2,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 5,
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "get-together",
        "_type" : "_doc",
        "_id" : "3",
        "_score" : 1.0,
        "_source" : {
          "relationship_type" : "group",
          "name" : "Elasticsearch San Francisco",
          "organizer" : "Mik",
          "description" : "Elasticsearch group for ES users of all knowledge levels",
          "created_on" : "2012-08-07",
          "tags" : [
            "elasticsearch",
            "big data",
            "lucene",
            "open source"
          ],
          "members" : [
            "Lee",
            "Igor"
          ],
          "location_group" : "San Francisco, California, USA"
        }
      },
      {
        "_index" : "get-together",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 1.0,
        "_source" : {
          "relationship_type" : "group",
          "name" : "Denver Clojure",
          "organizer" : [
            "Daniel",
            "Lee"
          ],
          "description" : "Group of Clojure enthusiasts from Denver who want to hack on code together and learn more about Clojure",
          "created_on" : "2012-06-15",
          "tags" : [
            "clojure",
            "denver",
            "functional programming",
            "jvm",
            "java"
          ],
          "members" : [
            "Lee",
            "Daniel",
            "Mike"
          ],
          "location_group" : "Denver, Colorado, USA"
        }
      },
     ...
```

### 查詢parent的id等於1的子文件
- 執行如下指令碼：

```shell
GET get-together/_search
{
  "query": {
    "parent_id": {
      "type": "event",
      "id": "1"
    }
  }
}
```

- 可以得到所有parent的id等於1的子文件：

```shell
{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 2,
    "successful" : 2,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 3,
    "max_score" : 1.3291359,
    "hits" : [
      {
        "_index" : "get-together",
        "_type" : "_doc",
        "_id" : "100",
        "_score" : 1.3291359,
        "_routing" : "1",
        "_source" : {
          "relationship_type" : {
            "name" : "event",
            "parent" : "1"
          },
          "host" : [
            "Lee",
            "Troy"
          ],
          "title" : "Liberator and Immutant",
          "description" : "We will discuss two different frameworks in Clojure for doing different things. Liberator is a ring-compatible web framework based on Erlang Webmachine. Immutant is an all-in-one enterprise application based on JBoss.",
          "attendees" : [
            "Lee",
            "Troy",
            "Daniel",
            "Tom"
          ],
          "date" : "2013-09-05T18:00",
          "location_event" : {
            "name" : "Stoneys Full Steam Tavern",
            "geolocation" : "39.752337,-105.00083"
          },
          "reviews" : 4
        }
      },
      ...
```

### 用script_fields簡化返回內容
- 前面的查詢，返回的內容是整個_source，如果不需要全部內容，可以用script_fields來簡化；
- 查詢所有父文件ID等1的的子文件，並且返回內容只有三個欄位：父文件ID、子文件ID、子文件title欄位：

```shell
GET get-together/_search
{
   "query": {
    "parent_id": {
      "type": "event",
      "id": "1"
    }
  },
  "script_fields":{
      "group_id":{
        "script":{
          "source":"doc['relationship_type#group']"
        }
      },"event_id":{
        "script":{
          "source":"doc['_id']"
        }
      },
      "title":{
        "script":"params['_source']['title']"
      }
    }
}
```
- 得到結果如下：

```shell
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 2,
    "successful" : 2,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 3,
    "max_score" : 1.3291359,
    "hits" : [
      {
        "_index" : "get-together",
        "_type" : "_doc",
        "_id" : "100",
        "_score" : 1.3291359,
        "_routing" : "1",
        "fields" : {
          "event_id" : [
            "100"
          ],
          "title" : [
            "Liberator and Immutant"
          ],
          "group_id" : [
            "1"
          ]
        }
      },
      {
        "_index" : "get-together",
        "_type" : "_doc",
        "_id" : "101",
        "_score" : 1.3291359,
        "_routing" : "1",
        "fields" : {
          "event_id" : [
            "101"
          ],
          "title" : [
            "Sunday, Surly Sunday"
          ],
          "group_id" : [
            "1"
          ]
        }
      },
      {
        "_index" : "get-together",
        "_type" : "_doc",
        "_id" : "102",
        "_score" : 1.3291359,
        "_routing" : "1",
        "fields" : {
          "event_id" : [
            "102"
          ],
          "title" : [
            "10 Clojure coding techniques you should know, and project openbike"
          ],
          "group_id" : [
            "1"
          ]
        }
      }
    ]
  }
}
```

### 聚合
- 執行以下查詢，會將所有父文件為group的子文件做桶聚合聚合：

```shell
GET get-together/_search
{
  "query": {
    "has_parent": {
      "parent_type": "group",
      "query": {
        "match_all": {}
      }
    }
  },
   "aggs":{
      "parents":{
        "terms":{
          "field":"relationship_type#group"
        }
      }
    }
}
```
- 得到的結果如下，按照父文件ID得到聚合結果：

```shell
"aggregations" : {
    "parents" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : "1",
          "doc_count" : 3
        },
        {
          "key" : "2",
          "doc_count" : 3
        },
        {
          "key" : "3",
          "doc_count" : 3
        },
        {
          "key" : "4",
          "doc_count" : 3
        },
        {
          "key" : "5",
          "doc_count" : 3
        }
      ]
    }
  }
}
```

- 以上就是join型別的主要實戰內容了，希望能幫助您理解這個新的型別；

### 歡迎關注ITpub：程式設計師欣宸
> [學習路上，你不孤單，欣宸原創一路相伴...](http://blog.itpub.net/70017844/)

實戰Elasticsearch6的join型別

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