Transactions and constraints

What this means

A transaction commits all included changes or rolls them back together. Constraints reject invalid data before it enters the database.

In beginner terms, this topic answers one practical question: "What should I write, and why does React care about it?" Do not try to memorize the syntax first. First understand the idea, then connect the syntax to that idea.

Why it matters

Payments, enrollment, inventory, and progress updates often require all-or-nothing consistency.

When you build real React screens, this idea helps you decide where data should live, what the user should see, and what should happen after an interaction. That is why this lesson is part of the main path instead of being an optional detail.

Step by step

1. Notice the UI problem this topic solves. 2. Look at the smallest possible example. 3. Change one value and predict what should appear. 4. Run the example and compare the result with your prediction. 5. Use the practice task before moving on.

Small example

BEGIN; UPDATE accounts ...; COMMIT;

Common mistake

Do not copy transactions and constraints syntax without explaining what problem it solves and checking the result.

Practice task

Change one part of the example, predict the result, run it, and explain the result in your own words.

Remember this

Transactions do not replace validation or careful isolation choices.