Transaction handling in Node.js - Step-by-Step Execution

Concept Flow - Transaction handling

Start Transaction

↓

Execute Queries

↓

Any Error?

Yes→Rollback Transaction

↓

Transaction Aborted

↓

Commit Transaction

↓

End

This flow shows starting a transaction, running queries, checking for errors, then either committing or rolling back.

Execution Sample

Node.js

async function runTransaction(db) {
  await db.beginTransaction();
  try {
    await db.query('INSERT INTO users ...');
    await db.commit();
  } catch (e) {
    await db.rollback();
  }
}

This code starts a transaction, runs a query, commits if successful, or rolls back on error.

Execution Table

Step	Action	Result	State Change	Next Step
1	Begin transaction	Transaction started	Transaction open	Execute queries
2	Run INSERT query	Query successful	Data staged	Check for errors
3	Check for errors	No error	Continue	Commit transaction
4	Commit transaction	Transaction committed	Data saved permanently	End
5	End	Transaction complete	Transaction closed	Stop

💡 Transaction ends after commit; all changes saved permanently.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	Final
transactionState	none	open	open	committed	closed
dataChanges	none	none	staged	saved	saved

Key Moments - 2 Insights

Why do we need to rollback the transaction on error?

Rollback undoes all changes made during the transaction to keep data consistent, as shown in step 4 of execution_table where commit only happens if no errors occur.

What happens if commit is called without starting a transaction?

Commit would fail or do nothing because there is no open transaction to finalize, as the transactionState variable shows 'none' before step 1.

Visual Quiz - 3 Questions

Look at the execution_table, what is the transactionState after step 2?

A closed

B committed

C open

D none

💡 Hint

Check variable_tracker row for transactionState after Step 2.

At which step does the transaction get permanently saved?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at execution_table row where commit happens.

If an error occurs during the query, what should happen next?

A Commit transaction

B Rollback transaction

C Ignore error and continue

D End without commit or rollback

💡 Hint

Refer to concept_flow where error leads to rollback.

Concept Snapshot

Transaction handling in Node.js:
- Start with db.beginTransaction()
- Run queries inside try block
- On success, call db.commit() to save changes
- On error, call db.rollback() to undo changes
- Ensures data stays consistent and safe

Full Transcript

Transaction handling means grouping database operations so they all succeed or fail together. In Node.js, you start a transaction with beginTransaction. Then you run your queries. If all queries succeed, you commit to save changes. If any query fails, you rollback to undo all changes. This keeps your data safe and consistent. The flow is: start transaction, run queries, check errors, commit if no errors, rollback if errors, then end.