$toUpper (aggregation)¶

Definition定义¶

$toUpper¶

Converts a string to uppercase, returning the result.

$toUpper has the following syntax:语法如下所示：

{ $toUpper: <expression> }

The argument can be any expression as long as it resolves to a string. For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。

If the argument resolves to null, $toUpper returns an empty string "".

Behavior行为¶

$toUpper only has a well-defined behavior for strings of ASCII characters.

Example示例¶

Consider a inventory collection with the following documents:考虑一个inventory集合带有以下文档：

{ "_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 }

The following operation uses the $toUpper operator return uppercase item and uppercase description values:

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

The operation returns the following results: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" : "" }