Database Manual / Reference / Query Language / Expressions

$strLenCP (expression operator)（表达式运算符）

Definition定义

$strLenCP

Returns the number of UTF-8 code points in the specified string.返回指定字符串中UTF-8码点数。

$strLenCP has the following operator expression syntax:$strLenCP具有以下运算符表达式语法：

{ $strLenCP: <string expression> }

The argument can be any valid expression that resolves to a string.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, $strLenCP returns an error.如果参数解析为null值或引用缺少的字段，$strLenCP将返回错误。

Example示例Results结果
{ $strLenCP: "abcde" }5
{ $strLenCP: "Hello World!" }12
{ $strLenCP: "cafeteria" }9
{ $strLenCP: "cafétéria" }9
{ $strLenCP: "" }0
{ $strLenCP: "$€λA" }4
{ $strLenCP: "寿司" }2

Behavior行为

The $strLenCP operator counts the number of code points in the specified string. This behavior differs from the $strLenBytes operator that counts the number of bytes in the string, where each character uses between one and four bytes.$strLenCP运算符计算指定字符串中的码点数。此行为与$strLenBytes运算符不同，后者计算字符串中的字节数，其中每个字符使用一到四个字节。

Example示例

Single-Byte and Multibyte Character Set单字节和多字节字符集

Create a food collection:创建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 $strLenCP operator to calculate the length of each name value:以下示例使用$strLenCP运算符计算每个name值的length：

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

Example output: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 }
]

Tip

$strLenBytes