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

The $ positional operator updates the first array element that matches the query condition. It acts as a placeholder for the matched array element's position.

Parameters

  • field.$: The array field with the positional operator to update the first matching element.

Example (MongoDB Shell)

The following example demonstrates using the $ positional operator to update a specific array element.

Create sample documents

db.inventory.insertMany([
  { _id: 1, item: "Widget", quantities: [10, 20, 30] },
  { _id: 2, item: "Gadget", quantities: [5, 15, 25] }
]);

Query example

db.inventory.updateOne(
  { _id: 1, quantities: 20 },
  { $set: { "quantities.$": 22 } }
);

Output

{
  "_id" : 1,
  "item" : "Widget",
  "quantities" : [ 10, 22, 30 ]
}

Code examples

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

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

async function updateDocument() {
  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('inventory');

  await collection.updateOne(
    { _id: 1, quantities: 20 },
    { $set: { "quantities.$": 22 } }
  );

  const updatedDocument = await collection.findOne({ _id: 1 });
  console.log(updatedDocument);

  await client.close();
}

updateDocument();
Python
from pymongo import MongoClient

def update_document():
    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.inventory

    collection.update_one(
        {'_id': 1, 'quantities': 20},
        {'$set': {'quantities.$': 22}}
    )

    updated_document = collection.find_one({'_id': 1})
    print(updated_document)

    client.close()

update_document()