$strLenCP (aggregation)¶

Definition定义¶

$strLenCP¶

New in version 3.4.版本3.4中的新功能。

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

$strLenCP has the following operator expression syntax:

{ $strLenCP: <string expression> }

The argument can be any valid expression as long as it resolves to an 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 a value of null or refers to a missing field, $strLenCP returns an error.

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 which counts the number of bytes in the string, where each character uses between one and four bytes.

Example示例¶

{ "_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 }