$toUpper (aggregation)

在本页面

Definition

  • $toUpper
    • 将字符串转换为大写,返回结果。

$toUpper具有以下语法:

{ $toUpper: <expression> }

参数可以是任何expression,只要它解析为字符串即可。有关表达式的更多信息,请参见Expressions

如果参数解析为 null,则$toLower返回空字符串""

Behavior

$toUpper仅对于 ASCII 字符字符串具有明确定义的行为。

Example

考虑包含以下文档的inventory集合:

{ "_id" : 1, "item" : "ABC1", quarter: "13Q1", "description" : "PRODUCT 1" }
{ "_id" : 2, "item" : "abc2", quarter: "13Q4", "description" : "Product 2" }
{ "_id" : 3, "item" : "xyz1", quarter: "14Q2", "description" : null }

以下操作使用$toUpper运算符返回大写item和大写description值:

db.inventory.aggregate(
   [
     {
       $project:
         {
           item: { $toUpper: "$item" },
           description: { $toUpper: "$description" }
         }
     }
   ]
)

该操作返回以下结果:

{ "_id" : 1, "item" : "ABC1", "description" : "PRODUCT 1" }
{ "_id" : 2, "item" : "ABC2", "description" : "PRODUCT 2" }
{ "_id" : 3, "item" : "XYZ1", "description" : "" }