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

The $unwind operator is used to deconstruct an array field from the input documents to output a document for each element. This can be useful when you want to perform operations on the individual elements of an array, such as filtering, sorting, or transforming the data.

Parameters

  • path: The path to the array field to be unwound.

  • includeArrayIndex: (optional) Specifies the name of the new field to hold the index of the array element.

  • preserveNullAndEmptyArrays: (optional) Determines whether the operation keeps the original document when the array field is null or an empty array.

Example (MongoDB Shell)

The following example demonstrates how to use the $unwind operator to deconstruct an array field and perform further operations on the individual elements.

Create sample documents

db.people.insertMany([
  { _id: 1, name: "jon", hobbies: ["painting", "dancing", "singing"] },
  { _id: 2, name: "jane", hobbies: ["reading", "swimming"] },
  { _id: 3, name: "jack", hobbies: [] }
])

Query example

db.people.aggregate([
  { $unwind: "$hobbies" }
])

Output

[
  { _id: 1, name: 'jon', hobbies: 'painting' },
  { _id: 1, name: 'jon', hobbies: 'dancing' },
  { _id: 1, name: 'jon', hobbies: 'singing' },
  { _id: 2, name: 'jane', hobbies: 'reading' },
  { _id: 2, name: 'jane', hobbies: 'swimming' }
]

Code examples

To view a code example for using the $unwind 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 collection = db.collection('people');

  const result = await collection.aggregate([
    { $unwind: '$hobbies' }
  ]).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']
    collection = db['people']

    result = list(collection.aggregate([
        { '$unwind': '$hobbies' }
    ]))

    print(result)
    client.close()

example()