Compound index and field order in MongoDB - Mini Project: Build & Apply

Creating and Using Compound Indexes in MongoDB

📖 Scenario: You are managing a MongoDB database for a small online bookstore. You want to speed up searches that look for books by both author and year of publication.

🎯 Goal: Build a compound index on the author and year fields in the books collection to improve query performance.

📋 What You'll Learn

Create a books collection with sample documents

Define a compound index on author and year fields

Understand the importance of field order in compound indexes

Query the collection using the compound index

💡 Why This Matters

🌍 Real World

Compound indexes help speed up searches that filter on multiple fields, common in real-world apps like bookstores, social media, and e-commerce.

💼 Career

Understanding compound indexes is essential for database administrators and backend developers to optimize query performance and resource usage.

1

Create the books collection with sample data

Create a collection called books and insert these exact documents: { title: "Book A", author: "Alice", year: 2020 }, { title: "Book B", author: "Bob", year: 2019 }, and { title: "Book C", author: "Alice", year: 2018 }.

MongoDB

// Insert the sample documents into the books collection
// Your code here

Need a hint?

Use db.books.insertMany() with an array of documents.

2

Define a compound index on author and year

Create a compound index on the books collection with author as the first field and year as the second field, both in ascending order.

MongoDB

db.books.insertMany([
  { title: "Book A", author: "Alice", year: 2020 },
  { title: "Book B", author: "Bob", year: 2019 },
  { title: "Book C", author: "Alice", year: 2018 }
])
// Create the compound index on author and year
// Your code here

Need a hint?

Use db.books.createIndex() with an object specifying author: 1 and year: 1.

3

Query using the compound index

Write a query to find all books where author is "Alice" and year is greater than or equal to 2019.

MongoDB

db.books.insertMany([
  { title: "Book A", author: "Alice", year: 2020 },
  { title: "Book B", author: "Bob", year: 2019 },
  { title: "Book C", author: "Alice", year: 2018 }
])
db.books.createIndex({ author: 1, year: 1 })
// Query books by author Alice and year >= 2019
// Your code here

Need a hint?

Use db.books.find() with a query object specifying author: "Alice" and year: { $gte: 2019 }.

4

Create a compound index with reversed field order

Create another compound index on the books collection with year as the first field and author as the second field, both in ascending order.

MongoDB

db.books.insertMany([
  { title: "Book A", author: "Alice", year: 2020 },
  { title: "Book B", author: "Bob", year: 2019 },
  { title: "Book C", author: "Alice", year: 2018 }
])
db.books.createIndex({ author: 1, year: 1 })
db.books.find({ author: "Alice", year: { $gte: 2019 } })
// Create a compound index with year first and author second
// Your code here

Need a hint?

Use db.books.createIndex() with { year: 1, author: 1 }.