文章目錄

• 概述
• 官方說明
• 例子

概述

繼續跟中華石杉老師學習ES，第26篇

課程地址： https://www.roncoo.com/view/55

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官方說明

https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-function-score-query.html

簡單來說： 自定義一個function_score函數，自己將某個field的值，跟es內置算出來的分數進行運算，然后由自己指定的field來進行分數的增強

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例子

需求： 看帖子的人越多，那么帖子的分數就越高

先給所有的帖子數據增加follower數量 ， 將對帖子搜索得到的分數，跟follower_num進行運算，由follower_num在一定程度上增強帖子的分數
看帖子的人越多，那么帖子的分數就越高

POST /forum/article/_bulk { "update": { "_id": "1"} } { "doc" : {"follower_num" : 5} } { "update": { "_id": "2"} } { "doc" : {"follower_num" : 10} } { "update": { "_id": "3"} } { "doc" : {"follower_num" : 25} } { "update": { "_id": "4"} } { "doc" : {"follower_num" : 3} } { "update": { "_id": "5"} } { "doc" : {"follower_num" : 60} }

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DSL

GET /forum/article/_search {"query": {"function_score": {"query": {"multi_match": {"query": "java spark","fields": ["tile", "content"]}},"field_value_factor": {"field": "follower_num","modifier": "log1p","factor": 0.5},"boost_mode": "sum","max_boost": 5}} }

• 如果只有field，那么會將每個doc的分數都乘以follower_num，如果有的doc follower是0，那么分數就會變為0，效果很不好。

• 因此一般會加個log1p函數，公式會變為，new_score = old_score * log(1 + number_of_votes)，這樣出來的分數會比較合理 。
  

• 再加個factor，可以進一步影響分數，new_score = old_score * log(1 + factor * number_of_votes)

• boost_mode，可以決定分數與指定字段的值如何計算 : multiply，replace, sum，min，max，avg

• max_boost，限制計算出來的分數不要超過max_boost指定的值
  

返回結果：

{"took": 87,"timed_out": false,"_shards": {"total": 1,"successful": 1,"skipped": 0,"failed": 0},"hits": {"total": 2,"max_score": 3.8050528,"hits": [{"_index": "forum","_type": "article","_id": "5","_score": 3.8050528,"_source": {"articleID": "DHJK-B-1395-#Ky5","userID": 3,"hidden": false,"postDate": "2019-05-01","tag": ["elasticsearch"],"tag_cnt": 1,"view_cnt": 10,"title": "this is spark blog","content": "spark is best big data solution based on scala ,an programming language similar to java spark","sub_title": "haha, hello world","author_first_name": "Tonny","author_last_name": "Peter Smith","new_author_last_name": "Peter Smith","new_author_first_name": "Tonny","follower_num": 60}},{"_index": "forum","_type": "article","_id": "2","_score": 1.7247463,"_source": {"articleID": "KDKE-B-9947-#kL5","userID": 1,"hidden": false,"postDate": "2017-01-02","tag": ["java"],"tag_cnt": 1,"view_cnt": 50,"title": "this is java blog","content": "i think java is the best programming language","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","follower_num": 10}}]} }

總結

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