TTL indexes for auto-expiry in MongoDB - Mini Project: Build & Apply

TTL Indexes for Auto-Expiry in MongoDB

📖 Scenario: You are managing a MongoDB database for a web application that stores temporary user session data. To keep the database clean and efficient, you want to automatically remove session documents after a certain time.

🎯 Goal: Build a MongoDB collection with a TTL index that automatically deletes session documents 3600 seconds (1 hour) after their creation.

📋 What You'll Learn

Create a collection named sessions with documents containing a createdAt field of type Date.

Add a TTL index on the createdAt field with an expiration time of 3600 seconds.

Insert a sample session document with the current date and time in createdAt.

Verify the TTL index is created correctly.

💡 Why This Matters

🌍 Real World

TTL indexes help automatically clean up temporary data like sessions, logs, or cache entries in databases, keeping storage efficient.

💼 Career

Understanding TTL indexes is useful for database administrators and backend developers managing data lifecycle and storage optimization.

1

Create the sessions collection and insert a session document

Create a collection called sessions and insert one document with a createdAt field set to the current date and time using new Date().

MongoDB

// Create the sessions collection and insert a document with createdAt
// Your code here

Need a hint?

Use db.sessions.insertOne({ createdAt: new Date() }) to insert the document.

2

Define the TTL index expiration time

Create a variable called expireAfterSeconds and set it to 3600 to represent the expiration time in seconds.

MongoDB

db.sessions.insertOne({ createdAt: new Date() })
// Define expireAfterSeconds variable
// Your code here

Need a hint?

Use const expireAfterSeconds = 3600 to set the expiration time.

3

Create the TTL index on createdAt

Use db.sessions.createIndex to create a TTL index on the createdAt field with the option { expireAfterSeconds: expireAfterSeconds }.

MongoDB

db.sessions.insertOne({ createdAt: new Date() })
const expireAfterSeconds = 3600
// Create TTL index on createdAt
// Your code here

Need a hint?

Use db.sessions.createIndex({ createdAt: 1 }, { expireAfterSeconds: expireAfterSeconds }) to create the TTL index.

4

Verify the TTL index creation

Use db.sessions.getIndexes() to list all indexes on the sessions collection and confirm the TTL index exists.

MongoDB

db.sessions.insertOne({ createdAt: new Date() })
const expireAfterSeconds = 3600
db.sessions.createIndex({ createdAt: 1 }, { expireAfterSeconds: expireAfterSeconds })
// Verify TTL index
// Your code here

Need a hint?

Use db.sessions.getIndexes() to see all indexes on the collection.