搜索引擎（Elasticsearch搜索详解-查询建议）

学习目标

掌握词项、短语查询建议器的用法
掌握自动补全建议器的用法
 

查询建议介绍

查询建议是什么？

ES中查询建议的API

查询建议也是使用_search端点地址。在DSL中suggest节点来定义须要的建议查询。

POST twitter/_search
{
  "query" : {
    "match": {
      "message": "tring out Elasticsearch"
    }
  },              //定义建议查询
  "suggest" : {
    "my-suggestion" : {          //一个建议查询名
      "text" : "tring out Elasticsearch",   //查询文本
      "term" : {                //使用词项建议器
        "field" : "message"     //指定在哪一个字段上获取建议词
      }
    }
  }
}

POST _search
{
  "suggest": {
    "my-suggest-1" : {
      "text" : "tring out Elasticsearch",
      "term" : {
        "field" : "message"
      }
    },
    "my-suggest-2" : {
      "text" : "kmichy",
      "term" : {
        "field" : "user"
      }
    }
  }
}

多个建议查询能够使用全局的查询文本

POST _search
{
  "suggest": {
    "text" : "tring out Elasticsearch",
    "my-suggest-1" : {
      "term" : {
        "field" : "message"
      }
    },
    "my-suggest-2" : {
       "term" : {
        "field" : "user"
       }
    }
  }
}

Suggester 介绍

Term suggester

term 词项建议器，对给入的文本进行分词，为每一个词进行模糊查询提供词项建议。对于在索引中存在词默认不提供建议词，不存在的词则根据模糊查询结果进行排序后取必定数量的建议词。

经常使用的建议选项：

phrase suggester

phrase 短语建议，在term的基础上，会考量多个term之间的关系，好比是否同时出如今索引的原文里，相邻程度，以及词频等

POST /ftq/_search
{
  "query": {
    "match_all": {}
  },
  
  "suggest" : {
    "myss":{
      "text": "java sprin boot",
      "phrase": {
        "field": "title"
      }
    }
  }
}

Completion suggester   自动补全

针对自动补全场景而设计的建议器。此场景下用户每输入一个字符的时候，就须要即时发送一次查询请求到后端查找匹配项，在用户输入速度较高的状况下对后端响应速度要求比较苛刻。所以实现上它和前面两个Suggester采用了不一样的数据结构，索引并不是经过倒排来完成，而是将analyze过的数据编码成FST和索引一块儿存放。对于一个open状态的索引，FST会被ES整个装载到内存里的，进行前缀查找速度极快。可是FST只能用于前缀查找，这也是Completion Suggester的局限所在。

https://www.elastic.co/guide/en/elasticsearch/reference/current/search-suggesters-completion.html

为了使用自动补全，索引中用来提供补全建议的字段需特殊设计，字段类型为 completion。

PUT music
{
    "mappings": {
        "_doc" : {
            "properties" : {
                "suggest" : {            //用于自动补全的字段
                    "type" : "completion"
                },
                "title" : {
                    "type": "keyword"
                }
            }
        }
    }
}

PUT music/_doc/1?refresh
{
    "suggest" : {
        "input": [ "Nevermind", "Nirvana" ],
        "weight" : 34
    }
}
Input 指定输入词
Weight 指定排序值（可选）

PUT music/_doc/1?refresh
{
    "suggest" : [
        {
            "input": "Nevermind",
            "weight" : 10
        },
        {
            "input": "Nirvana",
            "weight" : 3
        }
    ]}

PUT music/_doc/1?refresh
{
  "suggest" : [ "Nevermind", "Nirvana" ]
}

PUT music/_doc/2?refresh
{
    "suggest" : {     //放入一条重复数据
        "input": [ "Nevermind", "Nirvana" ],
        "weight" : 20
    }
}

POST music/_search?pretty
{
    "suggest": {
        "song-suggest" : {
            "prefix" : "nir", 
            "completion" : { 
                "field" : "suggest" 
            }
        }
    }
}

POST music/_search?pretty
{
    "suggest": {
        "song-suggest" : {
            "prefix" : "nir", 
            "completion" : { 
                "field" : "suggest",
                "skip_duplicates": true    //去重
            }
        }    }}

PUT music/_doc/3?refresh
{
    "suggest" : {
        "input": [ "lucene solr", "lucene so cool","lucene elasticsearch" ],
        "weight" : 20
    }   
}                   //存的是短语

PUT music/_doc/4?refresh
{
    "suggest" : {
        "input": ["lucene solr cool","lucene elasticsearch" ],
        "weight" : 10
    }
}

POST music/_search?pretty
{
    "suggest": {
        "song-suggest" : {
            "prefix" : "lucene s", 
            "completion" : { 
                "field" : "suggest" ,
                "skip_duplicates": true
            }
        }
    }
}