$strLenBytes (aggregation)

Definition

$strLenBytes

New in version 3.4.

Returns the number of UTF-8 encoded bytes in the specified string.

$strLenBytes has the following operator expression syntax:

{ $strLenBytes: <string expression> }

The argument can be any valid expression as long as it resolves to a string. For more information on expressions, see Expressions.

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

Behavior

The $strLenBytes operator counts the number of UTF-8 encoded bytes in a string where each character may use between one and four bytes.

For example, US-ASCII characters are encoded using one byte. Characters with diacritic markings and additional Latin alphabetical characters (Latin characters outside of the English alphabet) are encoded using two bytes. Chinese, Japanese and Korean characters typically require three bytes, and other planes of unicode (emoji, mathematical symbols, etc.) require four bytes.

The $strLenBytes operator differs from $strLenCP operator which counts the code points in the specified string regardless of how many bytes each character uses.

{ $strLenBytes: "abcde" }

{ $strLenBytes: "Hello World!" }

{ $strLenBytes: "cafeteria" }

{ $strLenBytes: "cafétéria" }

{ $strLenBytes: "" }

{ $strLenBytes: "$€λG" }

{ $strLenBytes: "寿司" }

Example

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": { $strLenBytes: "$name" }
      }
    }
  ]
)

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