Commit and abort behavior in MongoDB - Mini Project: Build & Apply

Commit and Abort Behavior in MongoDB Transactions

📖 Scenario: You are managing a small online bookstore database. You want to ensure that when a customer places an order, the stock quantity is updated only if the order is successfully recorded. If anything goes wrong, no changes should be saved.

🎯 Goal: Build a MongoDB transaction that inserts a new order and updates the stock quantity of a book. If any step fails, the transaction should abort, leaving the database unchanged.

📋 What You'll Learn

Create a MongoDB collection named books with a document for a book titled 'Learn MongoDB' with stock quantity 10.

Create a MongoDB collection named orders to store customer orders.

Start a session and a transaction.

Insert a new order document with customer name 'Alice' and book title 'Learn MongoDB'.

Update the stock quantity of 'Learn MongoDB' by reducing it by 1.

Commit the transaction if all operations succeed.

Abort the transaction if any operation fails.

💡 Why This Matters

🌍 Real World

Transactions ensure that multiple related database operations either all succeed or all fail, which is critical for applications like online stores to keep data consistent.

💼 Career

Understanding commit and abort behavior in MongoDB transactions is essential for backend developers and database administrators working with modern NoSQL databases.

1

Create the initial books collection with one book document

Create a MongoDB collection called books and insert one document with { title: 'Learn MongoDB', stock: 10 }.

MongoDB

// Your code here to create the books collection and insert the document

Need a hint?

Use insertOne on the books collection with the specified document.

2

Create the orders collection and start a session

Create a MongoDB collection called orders and start a client session with const session = db.getMongo().startSession().

MongoDB

db.books.insertOne({ title: 'Learn MongoDB', stock: 10 })
// Your code here to create orders collection and start session

Need a hint?

Use db.createCollection('orders') to create the orders collection and db.getMongo().startSession() to start a session.

3

Start a transaction and insert an order document

Use session.startTransaction() to begin a transaction. Then insert a document { customer: 'Alice', book: 'Learn MongoDB' } into the orders collection using the session.

MongoDB

db.books.insertOne({ title: 'Learn MongoDB', stock: 10 })
db.createCollection('orders')
const session = db.getMongo().startSession()
// Your code here to start transaction and insert order

Need a hint?

Call startTransaction() on the session, then insert the order document passing { session } as an option.

4

Update stock and commit or abort the transaction

Update the books collection to reduce the stock of 'Learn MongoDB' by 1 using the session. Then commit the transaction with session.commitTransaction(). If an error occurs, abort the transaction with session.abortTransaction().

MongoDB

db.books.insertOne({ title: 'Learn MongoDB', stock: 10 })
db.createCollection('orders')
const session = db.getMongo().startSession()
session.startTransaction()
db.orders.insertOne({ customer: 'Alice', book: 'Learn MongoDB' }, { session })
// Your code here to update stock and commit or abort transaction

Need a hint?

Use updateOne with $inc to reduce stock, then commit or abort the transaction inside a try-catch block.