15 使用copy_to定制组合field解决cross-fields搜索弊端

新增数据

PUT /forum/_mapping
{
  "properties": {
    "new_author_first_name": {
      "type": "text",
      "copy_to": "new_author_full_name"
    },
    "new_author_last_name": {
      "type": "text",
      "copy_to": "new_author_full_name"
    },
    "new_author_full_name": {
      "type": "text"
    }
  }
}

更新数据

POST /forum/article/_bulk
{ "update": { "_id": "1"} }
{ "doc" : {"new_author_first_name" : "Peter", "new_author_last_name" : "Smith"} }        
{ "update": { "_id": "2"} }    
{ "doc" : {"new_author_first_name" : "Smith", "new_author_last_name" : "Williams"} }        
{ "update": { "_id": "3"} }
{ "doc" : {"new_author_first_name" : "Jack", "new_author_last_name" : "Ma"} }            
{ "update": { "_id": "4"} }
{ "doc" : {"new_author_first_name" : "Robbin", "new_author_last_name" : "Li"} }            
{ "update": { "_id": "5"} }
{ "doc" : {"new_author_first_name" : "Tonny", "new_author_last_name" : "Peter Smith"} }    

查询

GET /forum/_search
{
  "query": {
    "match": {
      "new_author_full_name":"Peter Smith"
    }
  }
}

结果:

{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 2,
      "relation" : "eq"
    },
    "max_score" : 1.89712,
    "hits" : [
      {
        "_index" : "forum",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 1.89712,
        "_source" : {
          "articleID" : "XHDK-A-1293-#fJ3",
          "userID" : 1,
          "hidden" : false,
          "postDate" : "2017-01-01",
          "sub_title" : "learning more courses",
          "author_first_name" : "Peter",
          "author_last_name" : "Smith",
          "new_author_last_name" : "Smith",
          "new_author_first_name" : "Peter"
        }
      },
      {
        "_index" : "forum",
        "_type" : "_doc",
        "_id" : "2",
        "_score" : 0.6931472,
        "_source" : {
          "articleID" : "KDKE-B-9947-#kL5",
          "userID" : 1,
          "hidden" : false,
          "postDate" : "2017-01-02",
          "sub_title" : "learned a lot of course",
          "author_first_name" : "Smith",
          "author_last_name" : "Williams",
          "new_author_last_name" : "Williams",
          "new_author_first_name" : "Smith"
        }
      }
    ]
  }
}

• 问题1：只是找到尽可能多的field匹配的doc，而不是某个field完全匹配的doc

  答: 解决，最匹配的document被最先返回

• 问题2：most_fields，没办法用minimum_should_match去掉长尾数据，就是匹配的特别少的结果

  答: 解决，可以使用minimum_should_match去掉长尾数据

• 问题3：TF/IDF算法，比如Peter Smith和Smith Williams，搜索Peter
  Smith的时候，由于first_name中很少有Smith的，所以query在所有document中的频率很低，得到的分数很高，可能Smith Williams反而会排在Peter Smith前面

  答: 解决，Smith和Peter在一个field了，所以在所有document中出现的次数是均匀的，不会有极端的偏差