$strLenCP (aggregation)
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Definition定义
$strLenCP-
Returns the number of UTF-8 code points返回指定字符串中UTF-8代码点
in the specified string.的数目。$strLenCPhas the following operator expression syntax:具有以下运算符表达式语法：{ $strLenCP: <string expression> }The argument can be any valid expression that resolves to a string.参数可以是解析为字符串的任何有效表达式。If the argument resolves to a value of如果参数解析为nullor refers to a missing field,$strLenCPreturns an error.null值或引用了缺失的字段，$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. $strLenCP运算符统计指定字符串中的代码点数量。This behavior differs from the 此行为不同于统计字符串中字节数的$strLenBytes operator that counts the number of bytes in the string, where each character uses between one and four bytes.$strLenBytes运算符，其中每个字符使用一到四个字节。
Example实例
Single-Byte and Multibyte Character Set单字节和多字节字符集
Create a 创建food collection:food集合：
db.food.insertMany( [
{ _id: 1, name: "apple" },
{ _id: 2, name: "banana" },
{ _id: 3, name: "éclair" },
{ _id: 4, name: "hamburger" },
{ _id: 5, name: "jalapeño" },
{ _id: 6, name: "pizza" },
{ _id: 7, name: "tacos" },
{ _id: 8, name: "寿司" }
] )
The following example uses the 以下示例使用$strLenCP operator to calculate the length of each name value:$strLenCP运算符来计算每个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 }
]