Embedding vs referencing decision in MongoDB - Hands-On Comparison

Embedding vs Referencing Decision in MongoDB

📖 Scenario: You are building a simple online bookstore database using MongoDB. You want to store information about books and their authors. Each book has a title and an author. Each author has a name and a country.Sometimes authors write many books, and sometimes books have only one author. You want to decide whether to embed author details inside each book document or to reference authors separately.

🎯 Goal: Build two collections: authors and books. First, create author documents. Then create book documents that reference authors by their _id. This will help you understand referencing in MongoDB.

📋 What You'll Learn

Create an authors collection with two authors: 'Jane Austen' from 'UK' and 'Mark Twain' from 'USA'.

Create a books collection with two books: 'Pride and Prejudice' by Jane Austen and 'Adventures of Huckleberry Finn' by Mark Twain.

Use referencing by storing the author's _id inside each book document.

Do not embed author details inside the book documents.

💡 Why This Matters

🌍 Real World

Online bookstores and many other applications use referencing in MongoDB to keep data organized and avoid duplication.

💼 Career

Understanding embedding vs referencing is essential for designing efficient MongoDB databases in software development and data engineering roles.

1

Create the authors collection with two authors

Create a variable called authors that is a list of two dictionaries. The first dictionary should have 'name': 'Jane Austen' and 'country': 'UK'. The second dictionary should have 'name': 'Mark Twain' and 'country': 'USA'.

MongoDB

# Create the authors list with two author dictionaries
# Your code here

Need a hint?

Think of authors as a list of small address cards, each with a name and country.

2

Create a mapping from author names to their IDs

Create a variable called author_ids that is a dictionary mapping author names to unique string IDs. Use 'Jane Austen' mapped to 'a1' and 'Mark Twain' mapped to 'a2'.

MongoDB

authors = [
    {'name': 'Jane Austen', 'country': 'UK'},
    {'name': 'Mark Twain', 'country': 'USA'}
]
# Create a dictionary author_ids mapping author names to IDs
# Your code here

Need a hint?

This dictionary helps you link books to authors by ID instead of repeating full author details.

3

Create the books collection referencing authors by ID

Create a variable called books that is a list of two dictionaries. The first dictionary should have 'title': 'Pride and Prejudice' and 'author_id': 'a1'. The second dictionary should have 'title': 'Adventures of Huckleberry Finn' and 'author_id': 'a2'.

MongoDB

authors = [
    {'name': 'Jane Austen', 'country': 'UK'},
    {'name': 'Mark Twain', 'country': 'USA'}
]
author_ids = {'Jane Austen': 'a1', 'Mark Twain': 'a2'}
# Create the books list referencing authors by their IDs
# Your code here

Need a hint?

Each book stores only the author_id to link to the author, not the full author details.

4

Add the final step to simulate inserting documents into MongoDB

Create a variable called db that is an empty dictionary. Then add the authors list to db under the key 'authors' and the books list under the key 'books'.

MongoDB

authors = [
    {'name': 'Jane Austen', 'country': 'UK'},
    {'name': 'Mark Twain', 'country': 'USA'}
]
author_ids = {'Jane Austen': 'a1', 'Mark Twain': 'a2'}
books = [
    {'title': 'Pride and Prejudice', 'author_id': 'a1'},
    {'title': 'Adventures of Huckleberry Finn', 'author_id': 'a2'}
]
# Create a db dictionary and add authors and books collections
# Your code here

Need a hint?

This simulates how MongoDB stores collections inside a database object.