有时候需要对字段里面的字符串进行索引，比如查找评论，搜索引擎等需求。

• 全文搜索2.4以后默认开启，还在用以前版本的请自行百度Google开启全文搜索。
• 全文索引的建立比较慢，实操中需要等服务器闲时或者离线进行（否则会阻塞读写，当然也可以放在后台运行）。

使用

• 现在tesla集合有几条歌词文档数据如下:

{ "_id" : ObjectId("5a5b56b80f12feec77a93a86"), "song" : "1. Hotel California", "lyrics" : "On a dark desert highway, cool wind in my hair. Warm smell of colitas, rising up through the air.Chan" }
{ "_id" : ObjectId("5a5b56c00f12feec77a93a87"), "song" : "1. Hotel California", "lyrics" : "On a dark desert highway, cool wind in my hair. Warm smell of colitas, rising up through the air." }
{ "_id" : ObjectId("5a5b57200f12feec77a93a88"), "song" : "3. Hotel California", "lyrics" : "Such a lovely place, Such a lovely face." }
{ "_id" : ObjectId("5a5b57200f12feec77a93a89"), "song" : "4. Hotel California", "lyrics" : "Some dance to remember, some dance to forget." }
{ "_id" : ObjectId("5a5b57200f12feec77a93a8a"), "song" : "5. Hotel California", "lyrics" : "Welcome to the Hotel California" }
{ "_id" : ObjectId("5a5b57200f12feec77a93a8b"), "song" : "hell world", "lyrics" : "Welcome to beijing" }
{ "_id" : ObjectId("5a5b79090f12feec77a93a8c"), "song" : "6. Hotel California", "lyrics" : "ssl certificate" }
{ "_id" : ObjectId("5a5b7c080f12feec77a93a8d"), "song" : "7. Hotel California", "lyrics" : "pre-market lovely" }

添加全文索引：

db.tesla.ensureIndex({song:"text",lyrics:"text"},{weights:{song:1,lycris:2}})

{song:"text",lyrics:"text"}:给"song","lyrics"字段添加全文索引。
{weights:{song:1,lycris:2}: 权重分配，"lycris" 的权重为2，"song"的权重为1.(权重越大优先级越高，权重的区间为1-1000,000,000)
一旦分配错了权重，只能删除索引重新建立，建立权重请务必小心

• 搜索含有"lovely"的文档:

db.tesla.find({$text:{$search:"lovely"}})
{ "_id" : ObjectId("5a5b57200f128"), "song" : "3. Hotel California", "lyrics" : "Such a lovely place, Such a lovely face." }

(只有一条)

• 搜索含有"dark"的文档:

db.tesla.find({$text:{$search:"dark"}})
{ "_id" : ObjectId("5a5b56b80f126"), "song" : "1. Hotel California", "lyrics" : "On a dark desert highway, cool wind in my hair. Warm smell of colitas, rising up through the air. Chan" }
{ "_id" : ObjectId("5a5b56c00f167"), "song" : "1. Hotel California", "lyrics" : "On a dark desert highway, cool wind in my hair. Warm smell of colitas, rising up through the air." }

• 或搜索，搜索包含"lovely"或包含"remember"的文档：

db.tesla.find({$text:{$search:"lovely remember"}})
{ "_id" : ObjectId("5a5b57200f12feec77a93a88"), "song" : "3. Hotel California", "lyrics" : "Such a lovely place, Such a lovely face." }
{ "_id" : ObjectId("5a5b57200f12feec77a93a89"), "song" : "4. Hotel California", "lyrics" : "Some dance to remember, some dance to forget." }

(中间使用空格隔开)

• 与搜索，搜索包含"dark"和"Chan"的文档：

db.tesla.find({$text:{$search:"\"dark\"\"chan\""}})
{ "_id" : ObjectId("5a5b56b80f12feec77a93a86"), "song" : "1. Hotel California", "lyrics" : "On a dark desert highway, cool wind in my hair. Warm smell of colitas, rising up through the air.Chan" }

(使用\"把关键字包起来)

• 排除关键字，搜索包含"dark"但是不包含"Chan"的文档：

db.tesla.find({$text:{$search:"dark -chan"}})
{ "_id" : ObjectId("5a5b56c00f12feec77a93a87"), "song" : "1. Hotel California", "lyrics" : "On a dark desert highway, cool wind in my hair. Warm smell of colitas, rising up through the air." }

（使用-将排除的关键字标识出来）

• 排除关键字短语，例如pre-market，搜索含有"lovely"但是不包含"pre-market"的文档:

db.tesla.find({$text:{$search:"lovely -pre -market"}})
{ "_id" : ObjectId("5a5b57200f12feec77a93a88"), "song" : "3. Hotel California", "lyrics" : "Such a lovely place, Such a lovely face." }

(有短语的需要在短语之间进行拆分，例子中的pre-market拆成 pre -market，否则mongoDB会把pre-market的减号当成分隔符)

• A query can specify, at most, one $text expression.
• The $text query can not appear in $nor expressions.
• To use a $text query in an $or expression, all clauses in the $or array must be indexed.
• You cannot use hint() if the query includes a $text query expression.
• You cannot specify $natural sort order if the query includes a $text expression.
• You cannot combine the $text expression, which requires a special text index, with a query operator that requires a different type of special index. For example you cannot combine $text expression with the $near operator.
• Views do not support text search.

翻译：

• 一个查询只能指定最多一个$text表达式。
• $text表达式不能跟$nor一起使用。
• $text表达式跟$or一起使用的情况下，数组必须包含全文索引。
• 不能使用hint()强制指定使用全文搜索。
• 在$text表达式中不能使用{$natural:true}进行排序。
• 不能将$text表达式与可以允许不同类型的索引进行组合，例如不能将$text表达式跟$near操作符组合。
• View不支持全文索引。