$
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
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()
