Arithmetic expressions ($add, $multiply, $divide) in MongoDB - Mini Project: Build & Apply

Using Arithmetic Expressions in MongoDB Aggregation

📖 Scenario: You work in a small store that keeps product sales data in a MongoDB collection. You want to calculate the total revenue for each product by multiplying the quantity sold by the price per unit. You also want to add a fixed tax amount to the total revenue and then divide the final amount by 2 to find the average revenue over two months.

🎯 Goal: Build a MongoDB aggregation pipeline that uses the arithmetic expressions $add, $multiply, and $divide to calculate the average revenue including tax for each product.

📋 What You'll Learn

Create a collection named sales with documents containing product, quantity, and price fields.

Add a fixed tax amount variable named tax with the value 5.

Use $multiply to calculate total revenue by multiplying quantity and price.

Use $add to add the tax to the total revenue.

Use $divide to divide the sum by 2 to get the average revenue.

Output the product name and the calculated average revenue as averageRevenue.

💡 Why This Matters

🌍 Real World

Stores and businesses often need to calculate revenues, taxes, and averages from sales data stored in databases like MongoDB.

💼 Career

Understanding MongoDB aggregation and arithmetic expressions is essential for data analysts and backend developers working with NoSQL databases.

1

Create the sales collection with product data

Create a MongoDB collection named sales with these exact documents: { product: "Pen", quantity: 10, price: 2 }, { product: "Notebook", quantity: 5, price: 4 }, and { product: "Eraser", quantity: 20, price: 1 }.

MongoDB

// Insert the sales documents here
// Your code here

Need a hint?

Use db.sales.insertMany([...]) to add multiple documents at once.

2

Add a tax variable for the fixed tax amount

Create a variable named tax and set it to the number 5 to represent the fixed tax amount.

MongoDB

db.sales.insertMany([
  { product: "Pen", quantity: 10, price: 2 },
  { product: "Notebook", quantity: 5, price: 4 },
  { product: "Eraser", quantity: 20, price: 1 }
])

// Create the tax variable below
// Your code here

Need a hint?

Use const tax = 5 to create a fixed tax variable.

3

Calculate total revenue and add tax using $multiply and $add

Write a MongoDB aggregation pipeline that uses $multiply to multiply quantity and price to get total revenue, then uses $add to add the tax variable to this total. Use $project to output product and the calculated totalWithTax.

MongoDB

db.sales.insertMany([
  { product: "Pen", quantity: 10, price: 2 },
  { product: "Notebook", quantity: 5, price: 4 },
  { product: "Eraser", quantity: 20, price: 1 }
])

const tax = 5

// Write the aggregation pipeline below
// Your code here

Need a hint?

Use $project to create a new field totalWithTax that adds tax to the product of quantity and price.

4

Divide the total with tax by 2 using $divide to get average revenue

Extend the aggregation pipeline to use $divide to divide totalWithTax by 2. Output the product and the result as averageRevenue.

MongoDB

db.sales.insertMany([
  { product: "Pen", quantity: 10, price: 2 },
  { product: "Notebook", quantity: 5, price: 4 },
  { product: "Eraser", quantity: 20, price: 1 }
])

const tax = 5

db.sales.aggregate([
  {
    $project: {
      product: 1,
      totalWithTax: { $add: [ { $multiply: ["$quantity", "$price"] }, tax ] }
    }
  }
])

// Add $divide to calculate averageRevenue below
// Your code here

Need a hint?

Use $divide inside $project to divide the sum by 2 and rename the field to averageRevenue.