Elasticsearch(024)：es常见的字段映射类型之连接类型(join type)

红太狼 2023-07-23 03:44 27阅读 0赞

# join type概述 #

## 出现的背景 ##

*引出问题： “某头条新闻APP”新闻内容和新闻评论是1对多的关系？在ES6.X该如何存储、如何进行高效检索、聚合操作呢？*

## 1. **ES6.X 新类型join产生背景** ##

*  Mysql中多表关联，我们可以通过left join 或者Join等实现
 *  ES5.X版本，借助父子文档实现多表关联，类似数据库中Join的功能；实现的核心是借助于ES5.X支持1个索引(index)下多个类型(type)
 *  ES6.X版本，由于每个索引下面只支持单一的类型（type）
 *  所以，ES6.X版本如何实现Join成为关注点

ES6.X新推出了Join类型，**主要解决类似Mysql中多表关联的问题**。

## 2. **join类型介绍** ##

仍然是一个索引下，借助父子关系，实现类似Mysql中多表关联的操作

## 3. **join类型的mapping定义** ##

PUT my_index
    {
      "mappings": {
        "docs": {
          "properties": {
              "id": {
                "type": "long"
              },
              "my_join_field": { <1>
                "type": "join",
                "eager_global_ordinals": true,
                "relations": {
                  "question": "answer" <2>
                }
              },
              "text": {
                "type": "text",
                "fields": {
                  "keyword": {
                    "type": "keyword",
                    "ignore_above": 256
                  }
                }
              }
            }
        }
      }
    }

--------------------

<1> 为join的名称

<2> 指question为answer的父类

--------------------

## 4. **父文档数据插入** ##

PUT my_index/docs/1?refresh
    {
      "text": "This is a question",
      "my_join_field": {
        "name": "question" 
      }
    }
    
    PUT my_index/docs/2?refresh
    {
      "text": "This is a another question",
      "my_join_field": {
        "name": "question"
      }
    }
    
    PUT my_index/docs/_bulk?refresh
    {"index": {"_id": 3}}
    {"id":3, "text": "question 3333", "my_join_field": {"name": "question"}}
    {"index": {"_id": 4}}
    {"id":4, "text": "question 4444", "my_join_field": {"name": "question"}}

**文档类型为父类型: ”question”。**

## 5. **子类型文档插入** ##

PUT my_index/doc/5?routing=1&refresh <1>
    {
      "text": "This is an answer",
      "my_join_field": {
        "name": "answer", <2>
        "parent": "1" <3>
      }
    }
    
    PUT my_index/doc/6?routing=1&refresh
    {
      "text": "This is another answer",
      "my_join_field": {
        "name": "answer",
        "parent": "1"
      }
    }

--------------------

<1> 路由值是强制性的，因为父文件和子文件必须在相同的分片上建立索引。

<2> “answer”是此子文档的加入名称。代表其是一个子文档。

<3> 指定此子文档的父文档ID：1。

--------------------

## 6. 使用join类型的其他约束 ##

*  每个索引只允许一个Join类型Mapping定义
 *  父文档和子文档必须在同一个分片上编入索引；这意味着，当进行删除、更新、查找子文档时候需要提供**相同的路由值**
 *  一个文档可以有多个子文档，但只能有一个父文档
 *  可以为已经存在的Join类型添加新的关系
 *  当一个文档已经成为父文档后，可以为该文档添加子文档

## 7.**join类型的搜索与聚合** ##

### 7.1 **搜索全部** ###

GET my_index/docs/_search

结果数据为

{
      "took": 145,
      "timed_out": false,
      "_shards": {
        "total": 5,
        "successful": 5,
        "skipped": 0,
        "failed": 0
      },
      "hits": {
        "total": 6,
        "max_score": 1,
        "hits": [
          {
            "_index": "my_index",
            "_type": "docs",
            "_id": "4",
            "_score": 1,
            "_source": {
              "id": 4,
              "text": "question 4444",
              "my_join_field": {
                "name": "question"
              }
            }
          },
          {
            "_index": "my_index",
            "_type": "docs",
            "_id": "2",
            "_score": 1,
            "_source": {
              "text": "This is a another question",
              "my_join_field": {
                "name": "question"
              }
            }
          },
          {
            "_index": "my_index",
            "_type": "docs",
            "_id": "1",
            "_score": 1,
            "_source": {
              "text": "This is a question",
              "my_join_field": {
                "name": "question"
              }
            }
          },
          {
            "_index": "my_index",
            "_type": "docs",
            "_id": "5",
            "_score": 1,
            "_routing": "1",
            "_source": {
              "text": "This is an answer",
              "my_join_field": {
                "name": "answer",
                "parent": "1"
              }
            }
          },
          {
            "_index": "my_index",
            "_type": "docs",
            "_id": "6",
            "_score": 1,
            "_routing": "1",
            "_source": {
              "text": "This is another answer",
              "my_join_field": {
                "name": "answer",
                "parent": "1"
              }
            }
          },
          {
            "_index": "my_index",
            "_type": "docs",
            "_id": "3",
            "_score": 1,
            "_source": {
              "id": 3,
              "text": "question 3333",
              "my_join_field": {
                "name": "question"
              }
            }
          }
        ]
      }
    }

### 7.2 **基于父文档查找子文档** ###

GET my_index/docs/_search
    {
      "query": {
        "has_parent": {
          "parent_type": "question",
          "query": {
            "match": {
              "text": "this is"
            }
          }
        }
      }
    }

返回结果集

{
      "took": 161,
      "timed_out": false,
      "_shards": {
        "total": 5,
        "successful": 5,
        "skipped": 0,
        "failed": 0
      },
      "hits": {
        "total": 2,
        "max_score": 1,
        "hits": [
          {
            "_index": "my_index",
            "_type": "docs",
            "_id": "5",
            "_score": 1,
            "_routing": "1",
            "_source": {
              "text": "This is an answer",
              "my_join_field": {
                "name": "answer",
                "parent": "1"
              }
            }
          },
          {
            "_index": "my_index",
            "_type": "docs",
            "_id": "6",
            "_score": 1,
            "_routing": "1",
            "_source": {
              "text": "This is another answer",
              "my_join_field": {
                "name": "answer",
                "parent": "1"
              }
            }
          }
        ]
      }
    }

### 7.3 **基于子文档查找父文档** ###

GET my_index/docs/_search
    {
      "query": {
        "has_child": {
          "type": "answer",
          "query": {
            "match": {
              "text": "this is"
            }
          }
        }    
      }
    }

返回结果集

{
      "took": 286,
      "timed_out": false,
      "_shards": {
        "total": 5,
        "successful": 5,
        "skipped": 0,
        "failed": 0
      },
      "hits": {
        "total": 1,
        "max_score": 1,
        "hits": [
          {
            "_index": "my_index",
            "_type": "docs",
            "_id": "1",
            "_score": 1,
            "_source": {
              "text": "This is a question",
              "my_join_field": {
                "name": "question"
              }
            }
          }
        ]
      }
    }

### 7.4 **查找指定父文档id的子文档集合** ###

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

结果集

{
      "took": 3,
      "timed_out": false,
      "_shards": {
        "total": 5,
        "successful": 5,
        "skipped": 0,
        "failed": 0
      },
      "hits": {
        "total": 2,
        "max_score": 0.13353139,
        "hits": [
          {
            "_index": "my_index",
            "_type": "docs",
            "_id": "5",
            "_score": 0.13353139,
            "_routing": "1",
            "_source": {
              "text": "This is an answer",
              "my_join_field": {
                "name": "answer",
                "parent": "1"
              }
            }
          },
          {
            "_index": "my_index",
            "_type": "docs",
            "_id": "6",
            "_score": 0.13353139,
            "_routing": "1",
            "_source": {
              "text": "This is another answer",
              "my_join_field": {
                "name": "answer",
                "parent": "1"
              }
            }
          }
        ]
      }
    }

### 7.5 聚合操作 ###

在这里不做过多介绍，详细的使用方法请在后面的聚合的章节进行分析。