$substrBytes - Amazon DocumentDB
Example (MongoDB Shell)Code examples

$substrBytes

The $substrBytes operator in Amazon DocumentDB is used to extract a substring from a string based on a specified byte range. This operator is useful when you need to extract a substring from a string and the number of bytes required to represent each character in the string is important.

Unlike $substrCP, which operates on the number of Unicode code points, $substrBytes operates on the number of bytes required to represent the characters in the string. This can be particularly useful when working with strings that contain non-ASCII characters, as these characters may require more than one byte to represent.

*Note:* $substr has been deprecated since version 3.4. $substr is now an alias for $substrBytes.

Parameters

  • string: The input string from which the substring will be extracted.

  • startByte: The zero-based starting byte position of the substring to be extracted. A negative value can be used to specify a position from the end of the string.

  • length: The number of bytes in the substring to be extracted.

Example (MongoDB Shell)

In this example, we'll use $substrBytes to extract a substring from a string that contains non-ASCII characters.

Create sample documents

db.people.insertMany([
  { "_id": 1, "Desk": "Düsseldorf-NRW-021" },
  { "_id": 2, "Desk": "Bremerhaven-HBB-32a" },
  { "_id": 3, "Desk": "Norderstedt-SHH-892.50" },
  { "_id": 4, "Desk": "Brandenburg-BBB-78" }
]);

Query example

db.people.aggregate([
  {
    $project: {
      "state": { $substrBytes: [ "$Desk", 12, 3] }
    }
  }
])

Output

{ "_id": 1, "state": "NRW" },
{ "_id": 2, "state": "HBB" },
{ "_id": 3, "state": "SHH" },
{ "_id": 4, "state": "BBB" }

In this example, we use $substrBytes to extract a 3-byte substring starting from the 12th byte of the Desk field. This allows us to extract the 2-character state abbreviation, even though the string may contain non-ASCII characters.

Code examples

To view a code example for using the $substrBytes command, choose the tab for the language that you want to use:

Node.js
const { MongoClient } = require('mongodb');

async function example() {
  const client = await MongoClient.connect('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');
  const db = client.db('test');
  const people = db.collection('people');

  const result = await people.aggregate([
    {
      $project: {
        "state": { $substrBytes: ["$Desk", 12, 3] }
      }
    }
  ]).toArray();

  console.log(result);
  client.close();
}

example();
Python
from pymongo import MongoClient

def example():
    client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
    db = client.test
    people = db.people

    result = list(people.aggregate([
        {
            '$project': {
                "state": { '$substrBytes': ["$Desk", 12, 3] }
            }
        }
    ]))

    print(result)
    client.close()

example()