Transactions in NestJS - Mini Project: Build & Apply

Handling Transactions in NestJS

📖 Scenario: You are building a simple NestJS service to manage bank accounts. You want to ensure that money transfers between accounts happen safely using transactions, so that either both accounts update correctly or none do.

🎯 Goal: Build a NestJS service method that uses transactions to transfer money between two accounts safely.

📋 What You'll Learn

Create an initial accounts data structure with two accounts and their balances

Add a variable to hold the transfer amount

Write a service method that uses a transaction to update both accounts

Complete the transaction handling with commit and rollback logic

💡 Why This Matters

🌍 Real World

Transactions ensure that money transfers between accounts happen safely without data loss or corruption.

💼 Career

Understanding transactions is essential for backend developers working with databases and NestJS to build reliable financial or data-critical applications.

1

Create initial accounts data

Create a variable called accounts as a JavaScript object with two keys: accountA with value 1000 and accountB with value 500.

NestJS

// Create the accounts object with balances
// Your code here

Need a hint?

Use a JavaScript object with keys accountA and accountB and assign the given balances.

2

Add transfer amount variable

Add a constant variable called transferAmount and set it to 200.

NestJS

const accounts = { accountA: 1000, accountB: 500 };
// Define the transfer amount
// Your code here

Need a hint?

Use const transferAmount = 200; to define the amount to transfer.

3

Write transfer method with transaction

Write an async function called transferMoney that accepts no parameters. Inside, use a try block to simulate starting a transaction by logging 'Transaction started'. Then subtract transferAmount from accounts.accountA and add it to accounts.accountB. After that, log 'Transaction committed'. Add a catch block that logs 'Transaction rolled back' if an error occurs.

NestJS

const accounts = { accountA: 1000, accountB: 500 };
const transferAmount = 200;

// Write the transferMoney async function
// Your code here

Need a hint?

Use try and catch blocks inside an async function to simulate transaction behavior.

4

Complete transaction with NestJS style

Modify the transferMoney function to accept a queryRunner parameter. Use await queryRunner.startTransaction() at the start, then update the accounts. After updating, use await queryRunner.commitTransaction(). In the catch block, use await queryRunner.rollbackTransaction(). Finally, use await queryRunner.release() in a finally block.

NestJS

const accounts = { accountA: 1000, accountB: 500 };
const transferAmount = 200;

// Modify transferMoney to use queryRunner for transaction
// Your code here

Need a hint?

Use await with queryRunner methods to handle the transaction lifecycle properly.