Mongo技巧-连接数据库与修改表结构分析

java哥 阅读:167 2021-07-15 18:30:04 评论:0

1. 连接非本机数据库

mongo.exe之后直接输入ip地址即可

mongo.exe 192.168.163.203 

2. 修改表结构

mongo里面没有表结构这个概念,现在采用类似关系型数据库的形式来描述。如果想去掉collection里面的一个key,可以采用以下命令:

db.UserEntity.update({},{$unset:{Mail:1}},false,true); 

上面的命令从表UserEntity中删除一个字段Mail。

关于unset的具体说明

$unset 
The $unset operator deletes a particular field. Consider the following syntax: 
 
{ $unset: { <field1>: "", ... } } 
The specified value in the $unset expression (i.e. "") does not impact the operation. 
 
To specify a <field> in an embedded document or in an array, use dot notation. 
 
Behavior 
 
If the field does not exist, then $unset does nothing (i.e. no operation). 
 
When used with $ to match an array element, $unset replaces the matching element with null rather than removing the matching element from the array. This behavior keeps consistent the array size and element positions. 
 
Example 
 
The following update() operation uses the $unset operator to remove the fields quantity and instock from the first document in the products collection where the field sku has a value of unknown. 
 
db.products.update( 
   { sku: "unknown" }, 
   { $unset: { quantity: "", instock: "" } } 
) 
SEE ALSO 

标签:mongodb
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