Type conversion expressions ($toInt, $toString) in MongoDB - Mini Project: Build & Apply

Using $toInt and $toString in MongoDB Aggregation

📖 Scenario: You work at a small online store. The product prices are stored as strings in the database, but you need to calculate total prices as numbers for reports.

🎯 Goal: Build a MongoDB aggregation pipeline that converts price strings to integers using $toInt and then converts the total back to a string using $toString.

📋 What You'll Learn

Create a collection named products with documents containing name and price as strings.

Add a variable to hold the conversion target type.

Use $toInt to convert the price field to an integer.

Use $toString to convert the total price back to a string.

💡 Why This Matters

🌍 Real World

Many databases store numbers as strings for flexibility, but calculations require numeric types. Using $toInt and $toString helps convert data types during aggregation for accurate reports.

💼 Career

Data analysts and backend developers often need to convert data types in MongoDB to prepare data for calculations, reporting, and data cleaning.

1

Create the products collection with price strings

Create a collection called products with these exact documents: { name: "Pen", price: "10" }, { name: "Notebook", price: "25" }, and { name: "Eraser", price: "5" }.

MongoDB

// Insert the products documents here
// Your code here

Need a hint?

Use insertMany to add multiple documents to the products collection.

2

Add a variable for the target type conversion

Create a variable called targetType and set it to the string "int" to represent the integer conversion target.

MongoDB

db.products.insertMany([
  { name: "Pen", price: "10" },
  { name: "Notebook", price: "25" },
  { name: "Eraser", price: "5" }
])

// Create the targetType variable here
// Your code here

Need a hint?

Use const targetType = "int" to define the type for conversion.

3

Convert the price field to integer using $toInt

Write an aggregation pipeline that uses $addFields to add a new field priceInt which converts the price string to an integer using $toInt.

MongoDB

db.products.insertMany([
  { name: "Pen", price: "10" },
  { name: "Notebook", price: "25" },
  { name: "Eraser", price: "5" }
])

const targetType = "int"

// Add aggregation pipeline to convert price to integer
// Your code here

Need a hint?

Use $addFields to add priceInt and convert price with $toInt.

4

Convert the total price back to string using $toString

Extend the aggregation pipeline by adding a $group stage to sum all priceInt values into totalPrice, then add a $project stage to convert totalPrice to a string field called totalPriceString using $toString.

MongoDB

db.products.insertMany([
  { name: "Pen", price: "10" },
  { name: "Notebook", price: "25" },
  { name: "Eraser", price: "5" }
])

const targetType = "int"

const pipeline = [
  {
    $addFields: {
      priceInt: { $toInt: "$price" }
    }
  }
]

// Add $group and $project stages to sum priceInt and convert to string
// Your code here

Need a hint?

Use $group to sum priceInt and $project to convert the sum to string with $toString.