Transaction handling in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a transaction in the context of databases?

A transaction is a sequence of operations performed as a single logical unit of work. It ensures that either all operations succeed together or none do, keeping data consistent.

beginner

Name the four key properties of transactions (ACID).

Atomicity: All or nothing.<br>Consistency: Data stays valid.<br>Isolation: Transactions don’t interfere.<br>Durability: Changes are permanent once committed.

intermediate

How do you start a transaction using Node.js with a database client like 'pg' for PostgreSQL?

You call client.query('BEGIN') to start a transaction before running your queries.

beginner

What should you do if an error occurs during a transaction?

You should call client.query('ROLLBACK') to undo all changes made during the transaction to keep data consistent.

beginner

Why is transaction handling important in web applications?

It prevents partial updates that can cause data errors, especially when multiple users or processes access the database at the same time.

Which command starts a transaction in SQL?

A BEGIN

B COMMIT

C ROLLBACK

D SAVEPOINT

The BEGIN command starts a transaction block.

What does the COMMIT command do in a transaction?

A Saves all changes permanently

B Undoes all changes

C Starts a new transaction

D Locks the database

COMMIT saves all changes made during the transaction permanently.

In Node.js, which method is used to undo changes if a transaction fails?

A client.query('BEGIN')

B client.query('COMMIT')

C client.query('ROLLBACK')

D client.query('SAVEPOINT')

ROLLBACK undoes all changes made during the transaction.

Which ACID property ensures that transactions do not interfere with each other?

A Durability

B Isolation

C Atomicity

D Consistency

Isolation ensures transactions run independently without interference.

Why should you use transactions when multiple users update the same data?

A To speed up queries

B To reduce server memory

C To avoid using indexes

D To prevent partial updates and keep data consistent

Transactions prevent partial updates that can cause inconsistent data.

Explain how you would handle a transaction in Node.js using a database client.

Think about the sequence of commands to keep data safe.

Describe the ACID properties and why they matter for transaction handling.

These properties keep your data safe and reliable.