$mul operator for multiplication in MongoDB - Mini Project: Build & Apply

$mul Operator for Multiplication in MongoDB

📖 Scenario: You are managing a small online store's inventory database. You want to update the prices of some products by multiplying their current prices by a factor to apply a discount or increase.

🎯 Goal: Learn how to use the $mul operator in MongoDB to multiply numeric fields in documents.

📋 What You'll Learn

Create a collection named products with specific product documents.

Define a multiplication factor variable.

Use the $mul operator in an update query to multiply the price field of all products.

Verify the update by querying the collection.

💡 Why This Matters

🌍 Real World

Online stores often need to update prices in bulk due to sales, inflation, or supplier changes. Using $mul helps automate these updates efficiently.

💼 Career

Database administrators and backend developers use update operators like $mul to maintain and manipulate data in production databases.

1

Create the products collection with initial data

Create a MongoDB collection called products and insert these exact documents: { _id: 1, name: "Pen", price: 10 }, { _id: 2, name: "Notebook", price: 20 }, and { _id: 3, name: "Eraser", price: 5 }.

MongoDB

// Insert the specified documents into the products collection
// Your code here

Need a hint?

Use db.products.insertMany() with an array of objects to add multiple documents.

2

Define the multiplication factor

Create a variable called multiplier and set it to 1.1 to represent a 10% price increase.

MongoDB

db.products.insertMany([
  { _id: 1, name: "Pen", price: 10 },
  { _id: 2, name: "Notebook", price: 20 },
  { _id: 3, name: "Eraser", price: 5 }
])

// Create the multiplier variable
// Your code here

Need a hint?

Use const multiplier = 1.1 to define the multiplication factor.

3

Update all product prices using the $mul operator

Write an update query using db.products.updateMany() to multiply the price field of all documents by the multiplier variable using the $mul operator.

MongoDB

db.products.insertMany([
  { _id: 1, name: "Pen", price: 10 },
  { _id: 2, name: "Notebook", price: 20 },
  { _id: 3, name: "Eraser", price: 5 }
])

const multiplier = 1.1

// Update all prices by multiplying with multiplier
// Your code here

Need a hint?

Use db.products.updateMany({}, { $mul: { price: multiplier } }) to multiply prices.

4

Verify the updated prices

Write a query using db.products.find() to retrieve all documents and check that the price fields have been updated correctly.

MongoDB

db.products.insertMany([
  { _id: 1, name: "Pen", price: 10 },
  { _id: 2, name: "Notebook", price: 20 },
  { _id: 3, name: "Eraser", price: 5 }
])

const multiplier = 1.1

db.products.updateMany({}, { $mul: { price: multiplier } })

// Retrieve all products to verify updated prices
// Your code here

Need a hint?

Use db.products.find() to see all documents in the collection.