Why modeling decisions matter in MongoDB - See It in Action

Why Modeling Decisions Matter in MongoDB

📖 Scenario: You are working for a small online bookstore. You want to store information about books and their authors in a MongoDB database. How you decide to organize this data affects how easy it is to find and update information later.

🎯 Goal: Build a simple MongoDB collection that shows two different ways to model books and authors: embedding author details inside each book document, and referencing authors in a separate collection. This will help you understand why modeling decisions matter.

📋 What You'll Learn

Create a books collection with embedded author details.

Create an authors collection with author documents.

Create a books_ref collection where each book references an author by author_id.

Write queries to find books with embedded authors and books with referenced authors.

💡 Why This Matters

🌍 Real World

Choosing how to model data in MongoDB is important for building efficient and maintainable applications like online stores, blogs, or social networks.

💼 Career

Understanding data modeling helps database developers and backend engineers design databases that perform well and are easy to work with.

1

Create the books collection with embedded author details

Create a MongoDB collection called books and insert two documents. Each document should have the fields title and author. The author field should be an embedded document with name and birth_year. Use these exact entries: { title: "The Great Gatsby", author: { name: "F. Scott Fitzgerald", birth_year: 1896 } } and { title: "1984", author: { name: "George Orwell", birth_year: 1903 } }.

MongoDB

// Insert two books with embedded author details into the books collection
// Your code here

Need a hint?

Use db.books.insertMany() with an array of documents. Each document should have title and an embedded author document.

2

Create the authors collection with separate author documents

Create a MongoDB collection called authors and insert two documents. Each document should have the fields _id, name, and birth_year. Use these exact entries: { _id: 1, name: "F. Scott Fitzgerald", birth_year: 1896 } and { _id: 2, name: "George Orwell", birth_year: 1903 }.

MongoDB

db.books.insertMany([
  { title: "The Great Gatsby", author: { name: "F. Scott Fitzgerald", birth_year: 1896 } },
  { title: "1984", author: { name: "George Orwell", birth_year: 1903 } }
])
// Insert authors into the authors collection
// Your code here

Need a hint?

Use db.authors.insertMany() with an array of author documents. Each must have an _id field.

3

Create the books_ref collection with author references

Create a MongoDB collection called books_ref and insert two documents. Each document should have the fields title and author_id. Use these exact entries: { title: "The Great Gatsby", author_id: 1 } and { title: "1984", author_id: 2 }.

MongoDB

db.books.insertMany([
  { title: "The Great Gatsby", author: { name: "F. Scott Fitzgerald", birth_year: 1896 } },
  { title: "1984", author: { name: "George Orwell", birth_year: 1903 } }
])
db.authors.insertMany([
  { _id: 1, name: "F. Scott Fitzgerald", birth_year: 1896 },
  { _id: 2, name: "George Orwell", birth_year: 1903 }
])
// Insert books with author references into books_ref collection
// Your code here

Need a hint?

Use db.books_ref.insertMany() with documents that have title and author_id fields.

4

Query books with embedded authors and referenced authors

Write two queries: one to find all books in the books collection showing embedded author details, and one to find all books in the books_ref collection joined with author details from the authors collection using $lookup. Assign the results to variables embeddedBooks and referencedBooks respectively.

MongoDB

db.books.insertMany([
  { title: "The Great Gatsby", author: { name: "F. Scott Fitzgerald", birth_year: 1896 } },
  { title: "1984", author: { name: "George Orwell", birth_year: 1903 } }
])
db.authors.insertMany([
  { _id: 1, name: "F. Scott Fitzgerald", birth_year: 1896 },
  { _id: 2, name: "George Orwell", birth_year: 1903 }
])
db.books_ref.insertMany([
  { title: "The Great Gatsby", author_id: 1 },
  { title: "1984", author_id: 2 }
])
// Query embedded books
const embeddedBooks = db.books.find().toArray()
// Query referenced books with author details
const referencedBooks = db.books_ref.aggregate([
  { $lookup: {
      from: "authors",
      localField: "author_id",
      foreignField: "_id",
      as: "author"
  } },
  { $unwind: "$author" }
]).toArray()

Need a hint?

Use db.books.find().toArray() to get embedded books. Use db.books_ref.aggregate() with $lookup and $unwind to join authors.