Denormalization trade-offs in MongoDB - Mini Project: Build & Apply

Denormalization Trade-offs in MongoDB

📖 Scenario: You are building a simple online bookstore database using MongoDB. You want to understand how denormalization works by embedding author details directly inside book documents instead of referencing them separately.

🎯 Goal: Create a MongoDB collection with books that embed author information. Then add a configuration variable to control whether to embed or reference authors. Finally, write a query to retrieve books with embedded author details.

📋 What You'll Learn

Create a books collection with embedded author details

Add a variable embedAuthors to control embedding

Write a query to find all books with embedded author names

Add a final step to show how to switch between embedding and referencing

💡 Why This Matters

🌍 Real World

Denormalization by embedding related data is common in MongoDB to improve read performance by reducing the need for joins.

💼 Career

Understanding when to embed or reference data is key for designing efficient NoSQL databases in real-world applications.

1

Create the books collection with embedded authors

Create a MongoDB collection called books with two documents. Each document must have a title field and an embedded author field. The author field should be an object with name and birthYear. Use these exact values: First book: title "The Great Gatsby", author name "F. Scott Fitzgerald", birthYear 1896. Second book: title "1984", author name "George Orwell", birthYear 1903.

MongoDB

// Your code here to create the books collection with embedded authors

Need a hint?

Use db.books.insertMany() with an array of objects. Each object should have title and author fields. The author is an embedded object.

2

Add a variable embedAuthors to control embedding

Create a JavaScript variable called embedAuthors and set it to true. This variable will control if authors are embedded or referenced.

MongoDB

db.books.insertMany([
  {
    title: "The Great Gatsby",
    author: { name: "F. Scott Fitzgerald", birthYear: 1896 }
  },
  {
    title: "1984",
    author: { name: "George Orwell", birthYear: 1903 }
  }
])

// Your code here to add embedAuthors variable

Need a hint?

Use const embedAuthors = true to create the variable.

3

Write a query to find all books with embedded author names

Write a MongoDB query to find all documents in the books collection where the author.name field exists. Use db.books.find() with a filter that checks for author.name.

MongoDB

db.books.insertMany([
  {
    title: "The Great Gatsby",
    author: { name: "F. Scott Fitzgerald", birthYear: 1896 }
  },
  {
    title: "1984",
    author: { name: "George Orwell", birthYear: 1903 }
  }
])

const embedAuthors = true;

// Your code here to query books with embedded author names

Need a hint?

Use db.books.find({ "author.name": { $exists: true } }) to find books with embedded author names.

4

Add a final step to show switching between embedding and referencing

Add an if statement that checks if embedAuthors is true. If true, assign the embedded author object to a variable called bookAuthor. Otherwise, assign a reference ID string "authorId123" to bookAuthor.

MongoDB

db.books.insertMany([
  {
    title: "The Great Gatsby",
    author: { name: "F. Scott Fitzgerald", birthYear: 1896 }
  },
  {
    title: "1984",
    author: { name: "George Orwell", birthYear: 1903 }
  }
])

const embedAuthors = true;

db.books.find({ "author.name": { $exists: true } })

// Your code here to add if statement for embedding or referencing

Need a hint?

Use if (embedAuthors) { bookAuthor = {...} } else { bookAuthor = "authorId123" } to show the trade-off.