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操作符

$strLenCP (aggregation)

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定义

$strLenCP

Returns the number of UTF-8 code points in the specified string.

$strLenCP 具有以下操作符表达式语法：

{ $strLenCP: <string expression> }

The argument can be any valid 表达式(expression) that resolves to a string.

如果参数解析为 null 的值或指向缺失的字段，$strLenCP 返回错误。

例子
结果

{ $strLenCP: "abcde" }

5

{ $strLenCP: "Hello World!" }

12

{ $strLenCP: "cafeteria" }

9

{ $strLenCP: "cafétéria" }

9

{ $strLenCP: "" }

0

{ $strLenCP: "$€λA" }

4

{ $strLenCP: "寿司" }

2

行为

The $strLenCP operator counts the number of code points in the specified string. This behavior differs from the $strLenBytes operator that counts the number of bytes in the string, where each character uses between one and four bytes.

例子

单字节和多字节字符集

创建一个 food 集合：

db.food.insertMany( [
   { _id: 1, name: "apple" },
   { _id: 2, name: "banana" },
   { _id: 3, name: "éclair" },
   { _id: 4, name: "hamburger" },
   { _id: 5, name: "jalapeño" },
   { _id: 6, name: "pizza" },
   { _id: 7, name: "tacos" },
   { _id: 8, name: "寿司" }
] )

The following example uses the $strLenCP operator to calculate the length of each name value:

db.food.aggregate( [
   {
      $project: {
         name: 1,
         length: { $strLenCP: "$name" }
      }
   }
] )

示例输出：

[
   { _id: 1, name: 'apple', length: 5 },
   { _id: 2, name: 'banana', length: 6 },
   { _id: 3, name: 'éclair', length: 6 },
   { _id: 4, name: 'hamburger', length: 9 },
   { _id: 5, name: 'jalapeño', length: 8 },
   { _id: 6, name: 'pizza', length: 5 },
   { _id: 7, name: 'tacos', length: 5 },
   { _id: 8, name: '寿司', length: 2 }
]

另请参阅：

$strLenBytes

后退

$strLenBytes

来年

$substr

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