Trigger Recursion

trigger AccountTrigger on Account (after update) {
    for (Account acc : Trigger.new) {
        acc.Description = 'Last updated: ' + System.now();
    }
    update Trigger.new; // this update fires AccountTrigger again!
}

1. trigger AccountTrigger on Account (after update) { — an after update trigger.
2. for (Account acc : Trigger.new) { — loops over the just-saved records.
3. acc.Description = 'Last updated: ' + System.now(); — changes a field in memory.
4. } — closes the loop.
5. update Trigger.new; — performs a fresh update on Account records — this is Module 9's recursion concept, but happening accidentally through the trigger/DML relationship rather than a method deliberately calling itself.
6. } — closes the trigger.

public class AccountTriggerHandler {
    private static Boolean hasRun = false;

    public void afterUpdate(List<Account> updatedAccounts) {
        if (hasRun) {
            return;
        }
        hasRun = true;

        for (Account acc : updatedAccounts) {
            acc.Description = 'Last updated: ' + System.now();
        }
        update updatedAccounts;
    }
}

1. public class AccountTriggerHandler { — the handler class.
2. private static Boolean hasRun = false; — this is Module 10's static fields — one shared value per class, not per object — put to direct use.
3. (blank line)
4. public void afterUpdate(List<Account> updatedAccounts) { — the method.
5. if (hasRun) { — checks the guard first.
6. return; — hasRun persists across the recursive re-entry within the same transaction, so the second (recursive) call sees hasRun == true and exits immediately.
7. } — closes the if.
8. hasRun = true; — marks that this logic has now run.
9. (blank line)
10. for (Account acc : updatedAccounts) { — the same loop as before.
11. acc.Description = 'Last updated: ' + System.now(); — the same change.
12. } — closes the loop.
13. update updatedAccounts; — this update fires the trigger again, but the guard clause above stops it from updating and re-triggering a second time.
14. } — closes the method.
15. } — closes the class.

An unguarded recursive trigger typically shows up as a governor limit error — often "Too many DML statements" or "Apex CPU time limit exceeded" — from what looks like a single, simple update. If a trigger's error message mentions far more DML operations than the actual number of records being saved, unguarded recursion (rather than the SOQL/DML-in-a-loop problems from Module 7) is a strong suspect worth checking first.