elasticsearch实现like查询

绝地灬酷狼 2022-02-03 17:07 471阅读 0赞

## 问题 ##

elasticsearch查询需要实现类似于mysql的like查询效果，例如值为`hello中国233`的记录，即可以通过`中国`查询出记录，也可以通过`llo`查询出记录。

但是elasticsearch的查询都是基于分词查询，`hello中国233`会默认分词为`hello`、`中`、`国`、`233`。当使用`hello`查询时可以匹配到该记录，但是使用`llo`查询时，匹配不到该记录。

## 解决 ##

由于记录内容分词的结果的粒度不够细，导致分词查询匹配不到记录，因此解决方案是将记录内容以每个字符进行分词。即把`hello中国233`分词为`h`、`e`、`l`、`o`、`中`、`国`、`2`、`3`。

elasticsearch默认没有如上效果的分词器，可以通过自定义分词器实现该效果：通过字符过滤器，将字符串的每一个字符间添加一个空格，再使用空格分词器将字符串拆分成字符。

## 效果 ##

#### 默认分词 ####

PUT /like_search
    { 
      "mappings": { 
        "like_search_type": { 
          "properties": { 
            "name": { 
              "type": "text"
            }
          }
        }
      }
    }
    
    PUT /like_search/like_search_type/1
    { 
      "name": "hello中国233"
    }

分词效果

GET /like_search/_analyze
    { 
      "text": [
        "hello中国233"
        ]
    }

{ 
      "tokens": [
        { 
          "token": "hello",
          "start_offset": 0,
          "end_offset": 5,
          "type": "<ALPHANUM>",
          "position": 0
        },
        { 
          "token": "中",
          "start_offset": 5,
          "end_offset": 6,
          "type": "<IDEOGRAPHIC>",
          "position": 1
        },
        { 
          "token": "国",
          "start_offset": 6,
          "end_offset": 7,
          "type": "<IDEOGRAPHIC>",
          "position": 2
        },
        { 
          "token": "233",
          "start_offset": 7,
          "end_offset": 10,
          "type": "<NUM>",
          "position": 3
        }
      ]
    }

elasticsearch默认使用`standard`分词器，如下通过`llo`查询不到`hello中国233`的记录。

GET /like_search/_search
    { 
      "query": { 
        "match_phrase": { 
          "name": "llo"
        }
      }
    }

#### 自定义分词 ####

PUT /like_search
    { 
      "settings": { 
        "analysis": { 
          "analyzer": { 
            "char_analyzer": { 
              "char_filter": [
                "split_by_whitespace_filter"
              ],
              "tokenizer": "whitespace"
            }
          },
          "char_filter": { 
            "split_by_whitespace_filter": { 
              "type": "pattern_replace",
              "pattern": "(.+?)",
              "replacement": "$1 "
            }
          }
        }
      },
      "mappings": { 
        "like_search_type": { 
          "properties": { 
            "name": { 
              "type": "text",
              "analyzer": "char_analyzer"
            }
          }
        }
      }
    }
    
    PUT /like_search/like_search_type/1
    { 
      "name": "hello中国233"
    }

分词效果

GET /like_search/_analyze
    { 
      "analyzer": "char_analyzer", 
      "text": [
        "hello中国233"
        ]
    }

{ 
      "tokens": [
        { 
          "token": "h",
          "start_offset": 0,
          "end_offset": 0,
          "type": "word",
          "position": 0
        },
        { 
          "token": "e",
          "start_offset": 1,
          "end_offset": 1,
          "type": "word",
          "position": 1
        },
        { 
          "token": "l",
          "start_offset": 2,
          "end_offset": 2,
          "type": "word",
          "position": 2
        },
        { 
          "token": "l",
          "start_offset": 3,
          "end_offset": 3,
          "type": "word",
          "position": 3
        },
        { 
          "token": "o",
          "start_offset": 4,
          "end_offset": 4,
          "type": "word",
          "position": 4
        },
        { 
          "token": "中",
          "start_offset": 5,
          "end_offset": 5,
          "type": "word",
          "position": 5
        },
        { 
          "token": "国",
          "start_offset": 6,
          "end_offset": 6,
          "type": "word",
          "position": 6
        },
        { 
          "token": "2",
          "start_offset": 7,
          "end_offset": 7,
          "type": "word",
          "position": 7
        },
        { 
          "token": "3",
          "start_offset": 8,
          "end_offset": 8,
          "type": "word",
          "position": 8
        },
        { 
          "token": "3",
          "start_offset": 9,
          "end_offset": 9,
          "type": "word",
          "position": 9
        }
      ]
    }

使用自定义的分词器，如下通过`llo`可以查询到`hello中国233`的记录。

GET /like_search/_search
    { 
      "query": { 
        "match_phrase": { 
          "name": "llo"
        }
      }
    }