String expressions ($concat, $toUpper, $toLower) in MongoDB - Mini Project: Build & Apply

Using String Expressions in MongoDB Aggregation

📖 Scenario: You work in a small bookstore's database team. The store keeps records of books with separate fields for the author's first name and last name. You want to create a new field that shows the author's full name in uppercase letters for better display on the website.

🎯 Goal: Build a MongoDB aggregation pipeline that combines the author's first and last names into a single full name string, converts it to uppercase, and stores it in a new field called authorFullName.

📋 What You'll Learn

Create a collection named books with documents containing authorFirstName and authorLastName fields.

Add a configuration variable space that holds a single space character.

Use the $concat expression to join the first name, space, and last name into one string.

Use the $toUpper expression to convert the concatenated full name to uppercase.

Add the resulting uppercase full name as a new field authorFullName in the aggregation output.

💡 Why This Matters

🌍 Real World

Bookstores and libraries often store author names in separate fields. Combining and formatting these names helps display them nicely on websites and reports.

💼 Career

Database developers and data engineers frequently use string expressions in MongoDB aggregation pipelines to transform and prepare data for applications.

1

Create the books collection with author names

Create a MongoDB collection called books with these exact documents: { authorFirstName: "Jane", authorLastName: "Austen" } and { authorFirstName: "Mark", authorLastName: "Twain" }.

MongoDB

// Insert the two book documents into the books collection
// Your code here

Need a hint?

Use insertMany to add multiple documents to the books collection.

2

Add a space variable for joining names

Create a variable called space and set it to a string containing a single space character " ".

MongoDB

db.books.insertMany([
  { authorFirstName: "Jane", authorLastName: "Austen" },
  { authorFirstName: "Mark", authorLastName: "Twain" }
])

// Create a variable called space with a single space string
// Your code here

Need a hint?

Use const space = " " to store a space character.

3

Use $concat to join first and last names with space

Write a MongoDB aggregation pipeline stage that uses $concat to join authorFirstName, the variable space, and authorLastName into a new field called fullName.

MongoDB

db.books.insertMany([
  { authorFirstName: "Jane", authorLastName: "Austen" },
  { authorFirstName: "Mark", authorLastName: "Twain" }
])

const space = " "

// Create an aggregation pipeline stage that adds fullName by concatenating authorFirstName, space, and authorLastName
// Your code here

Need a hint?

Use $addFields with $concat to join the fields and the space variable.

4

Convert the full name to uppercase with $toUpper

Extend the aggregation pipeline to add a new field called authorFullName that converts the fullName field to uppercase using $toUpper.

MongoDB

db.books.insertMany([
  { authorFirstName: "Jane", authorLastName: "Austen" },
  { authorFirstName: "Mark", authorLastName: "Twain" }
])

const space = " "

const pipeline = [
  {
    $addFields: {
      fullName: { $concat: ["$authorFirstName", space, "$authorLastName"] }
    }
  }
]

// Add authorFullName field that converts fullName to uppercase
// Your code here

Need a hint?

Use $toUpper around the fullName field to create authorFullName.