$strLenCP（表达式操作符）

定义

$strLenCP

返回指定字符串中 UTF-8 代码点的数量。

$strLenCP has the following operator expression syntax:

{ $strLenCP: <string expression> }

该参数可以是解析为字符串的任何有效表达式。

If the argument resolves to a value of null or refers to a missing field, $strLenCP returns an error.

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

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" }
] )

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

[
   { _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 }
]