MongoDB 索引之全文索引

末蓝、 2022-08-07 06:46 291阅读 0赞

mongodb full text search(fts：全文搜素)是在版本2.4新加的特性。在以前的版本，是通过精确匹配和正则表达式来查询，这效率是很低的。全文索引，能够从大量的文本中搜索出所需的内容，内置多国语言和分词方法。不支持宇宙第一语言—中文。全文索引会导致mongodb写入性能下降，因为所有字符串都要拆分，存储到不同地方。   
全文索引是一种技术，并大量的使用。如搜索引擎，站内搜索等等。常使用到的全文搜索有：   
lucene   
sphinx   
redis-search   
riak search   
不过，对中文的搜索不尽如人意。   
mongodb用的是开源的snowball分词器。参见 [http://snowball.tartarus.org/texts/stemmersoverview.html][http_snowball.tartarus.org_texts_stemmersoverview.html]  
mongodb 全文索引支持的语言有：   
danish   
dutch   
english   
finnish   
french   
german   
hungarian   
italian   
norwegian   
portuguese   
romanian   
russian   
spanish   
swedish   
turkish   
如果希望使用其他语言，需要在创建索引时指定要使用的语言。默认是支持英文的。   
>db.collection.ensureIndex(\{content:"text"\},\{default\_language:"spanish"\})   
**一、开启全文索引 **  
默认是关闭的。否则会报错"err" : "text search not enabled"   
可以在脚本中声明启用:   
> db.adminCommand(\{setParameter:1,textSearchEnabled:true\})   
\{ "was" : true, "ok" : 1 \}   
也修改配置启用:mongod --setParameter textSearchEnabled=true   
**二、插入测试数据 **  
下面是插入一些《加州旅馆》这首二十世纪非常著名的流行音乐。

> db.ttlsa_com.insert({"song":"1. Hotel California", "lyrics": "On a dark desert highway, cool wind in my hair. Warm smell of colitas, rising up through the air."}) 
    > db.ttlsa_com.insert({"song":"2. Hotel California", "lyrics": "Up ahead in the distance, I saw a shimmering light. My head grew heavy and my sight grew dim."}) 
    > db.ttlsa_com.insert({"song":"3. Hotel California", "lyrics": "Such a lovely place, Such a lovely face."}) 
    > db.ttlsa_com.insert({"song":"4. Hotel California", "lyrics": "Some dance to remember, some dance to forget."}) 
    > db.ttlsa_com.insert({"song":"5. Hotel California", "lyrics": "Welcome to the Hotel California"}) 
    > db.ttlsa_com.insert({"song":"hell world", "lyrics": "Welcome to beijing"})

> db.ttlsa\_com.insert(\{"song":"加州旅馆", "lyrics": "Welcome to the Hotel California"\})   
**三、创建全文索引 **  
> db.ttlsa\_com.ensureIndex(\{"song":"text", "lyrics":"text"\})   
或者   
> db.ttlsa\_com.ensureIndex(\{"$\*\*": "text"\})   
$\*\*表示在所有的字符串字段上创建一个全文索引。   
也可以指定权重   
> db.ttlsa\_com.ensureIndex(\{"song":"text"\},\{"weights":\{"song": 2, "$\*\*": 3\}\})   
**四、查看索引信息 **

>db.system.indexes.find().toArray() 
    [{
    "v": 1,
    "key": {
    "_id": 1
    },
    "name": "_id_",
    "ns": "test.ttlsa_com"
    },
    {
    "v": 1,
    "key": {
    "_fts": "text",
    "_ftsx": 1
    },
    "name": "song__lyrics_",
    "ns": "test.ttlsa_com",
    "weights": {
    "lyrics": 1,
    "song": 1
    },
    "default_language": "english",
    "language_override": "language",
    "textIndexVersion": 2
    }]

**五、查询 **  
全文索引是通过   
db.collection.runCommand( "text", \{ search: <string>,   
filter: <document>,   
project: <document>,   
limit: <number>,   
language: <string> \} )   
来查询的，非通过find()命令来实现的。 也可以通过find查询，如：db.ttlsa\_com.find(\{$text:\{$search:"aa bb"\}\});  
1.搜索一个词，文本命令是不区分大小写的

> db.ttlsa_com.runCommand("text",{search:"Welcome"}) 
    { 
    "results" : [ 
    { 
    "score" : 0.6666666666666666, 
    "obj" : { 
    "_id" : ObjectId("550a615dd8511e4dbcb8c77a"), 
    "song" : "5. Hotel California", 
    "lyrics" : "Welcome to the Hotel California" 
    } 
    }, 
    { 
    "score" : 0.6666666666666666, 
    "obj" : { 
    "_id" : ObjectId("550a6163d8511e4dbcb8c77b"), 
    "song" : "加州旅馆", 
    "lyrics" : "Welcome to the Hotel California" 
    } 
    } 
    ], 
    "stats" : { 
    "nscanned" : 2, 
    "nscannedObjects" : 2, 
    "n" : 2, 
    "timeMicros" : 1486, 
    "shards" : { 
    "shard_a" : { 
    "nscanned" : NumberLong(2), 
    "nscannedObjects" : NumberLong(2), 
    "n" : 2, 
    "timeMicros" : 917 
    } 
    } 
    }, 
    "ok" : 1 
    }

2.模糊搜索

> db.ttlsa_com.runCommand("text",{search:"Such lovely"}) 
    { 
    "results" : [ 
    { 
    "score" : 1.125, 
    "obj" : { 
    "_id" : ObjectId("550a6154d8511e4dbcb8c778"), 
    "song" : "3. Hotel California", 
    "lyrics" : "Such a lovely place, Such a lovely face." 
    } 
    } 
    ], 
    "stats" : { 
    "nscanned" : 1, 
    "nscannedObjects" : 1, 
    "n" : 1, 
    "timeMicros" : 618, 
    "shards" : { 
    "shard_a" : { 
    "nscanned" : NumberLong(1), 
    "nscannedObjects" : NumberLong(1), 
    "n" : 1, 
    "timeMicros" : 272 
    } 
    } 
    }, 
    "ok" : 1 
    }

3.匹配短语

> db.ttlsa_com.runCommand("text",{search:"\"Some dance to remember\""}) 
    { 
    "results" : [ 
    { 
    "score" : 1.75, 
    "obj" : { 
    "_id" : ObjectId("550a6158d8511e4dbcb8c779"), 
    "song" : "4. Hotel California", 
    "lyrics" : "Some dance to remember, some dance to forget." 
    } 
    } 
    ], 
    "stats" : { 
    "nscanned" : 2, 
    "nscannedObjects" : 1, 
    "n" : 1, 
    "timeMicros" : 743, 
    "shards" : { 
    "shard_a" : { 
    "nscanned" : NumberLong(2), 
    "nscannedObjects" : NumberLong(1), 
    "n" : 1, 
    "timeMicros" : 306 
    } 
    } 
    }, 
    "ok" : 1 
    }

4.匹配一些词但是不能包含指定的词

> db.ttlsa_com.runCommand("text",{search:"Welcome -California"}) 
    { 
    "results" : [ 
    { 
    "score" : 0.75, 
    "obj" : { 
    "_id" : ObjectId("550a687fd8511e4dbcb8c781"), 
    "song" : "hell world", 
    "lyrics" : "Welcome to beijing" 
    } 
    } 
    ], 
    "stats" : { 
    "nscanned" : 4, 
    "nscannedObjects" : 4, 
    "n" : 1, 
    "timeMicros" : 743, 
    "shards" : { 
    "shard_a" : { 
    "nscanned" : NumberLong(4), 
    "nscannedObjects" : NumberLong(4), 
    "n" : 1, 
    "timeMicros" : 345 
    } 
    } 
    }, 
    "ok" : 1 
    }

5.限制结果集条目   
>db.ttlsa\_com.runCommand("text",\{search:"Welcome",limit: 1\})   
6.在结果集中指定返回的字段   
>db.ttlsa\_com.runCommand("text",\{search:"Welcome",project:\{"song":1,"\_id":0\}\})   
7.带额外查询条件的搜索   
>db.ttlsa\_com.runCommand("text",\{search:"Welcome",filter: \{"song":"hell world"\}\})   
8.使用特定语言搜索文本   
>db.ttlsa\_com.runCommand("text",\{search:"Welcome",language:"spanish"\})   
9.分词效果不是很理想。如

>db.ttlsa_com.runCommand("text",{search:"the"}) 
    { 
    "results" : [ ], 
    "stats" : { 
    "nscanned" : 0, 
    "nscannedObjects" : 0, 
    "n" : 0, 
    "timeMicros" : 432, 
    "shards" : { 
    "shard_a" : { 
    "nscanned" : NumberLong(0), 
    "nscannedObjects" : NumberLong(0), 
    "n" : 0, 
    "timeMicros" : 151 
    } 
    } 
    }, 
    "ok" : 1 
    }

就搜索不到的。   
mongodb是不支持中文搜索的。 全文索引可以通过相似度，来查询与条件更匹配的文章，如下：

>db. ttlsa\_com.find(\{$text:\{$search:"aa bb"\}\},\{score:\{$meta:"textScore"\}\})  
查询结果返回相似度分数。可以结合sort进行相似度排序。

>db. ttlsa\_com.find(\{$text:\{$search:"aa bb"\}\},\{score:\{$meta:"textScore"\}\}).sort(\{score:\{$meta:"textScore"\}\});

要用到复杂的搜索功能，还是用sphinx。   
sphinx内容可以参见： [http://www.ttlsa.com/?s=sphinx][http_www.ttlsa.com_s_sphinx]

详细使用参考： [http://blog.csdn.net/black\_ox/article/details/21547651][http_blog.csdn.net_black_ox_article_details_21547651]  
  
转至： [http://www.ttlsa.com/mongodb/mongodb-full-text-search-mongodb-ttlsa-tutorial-series/][http_www.ttlsa.com_mongodb_mongodb-full-text-search-mongodb-ttlsa-tutorial-series]

[http_snowball.tartarus.org_texts_stemmersoverview.html]: http://snowball.tartarus.org/texts/stemmersoverview.html
[http_www.ttlsa.com_s_sphinx]: http://www.ttlsa.com/?s=sphinx
[http_blog.csdn.net_black_ox_article_details_21547651]: http://blog.csdn.net/black_ox/article/details/21547651
[http_www.ttlsa.com_mongodb_mongodb-full-text-search-mongodb-ttlsa-tutorial-series]: http://www.ttlsa.com/mongodb/mongodb-full-text-search-mongodb-ttlsa-tutorial-series/