Say I want to prove to myself that when I delete a detail record, the master record is locked. How would I do that?

  • In another transaction - DML on the master or acquire lock with FOR UPDATE
    – identigral
    Oct 2, 2022 at 20:01

1 Answer 1


I demonstrate a similar concept in this answer, but the basic idea is to write a Visualforce page that calls two simultaneous apex:actionFunction methods. For example, you could have the first method delete the detail record, then spin for 10 seconds, while the second method spins for, say, 1 second, then attempt to update the parent record. This might get you started:

public class TestRecordLock {
    Account theAccount;
    Contact theContact;
    public void initializeData() {
        theAccount = new Account(Name='Demo');
        insert theAccount;
        theContact = new Contact(LastName='Demo', AccountId=theAccount.Id);
        insert theContact;
    void sleep(Integer ms) {
        Long startTime = DateTime.now().getTime();
    public void deleteContact() {
        delete theContact;
        sleep(10000); // 10 seconds
    public void updateAccount() {
        sleep(1000); // Small delay, just to be safe.
        update theAccount;

<apex:page controller="TestRecordLock" action="{!initializeData}">
        <apex:actionFunction name="deleteTheContact" action="{!deleteContact}" reRender="" />
        <apex:actionFunction name="updateTheAccount" action="{!updateAccount}" reRender="" />
    window.addEventListener('load', () => {

Because DML forces a lock to be acquired, if you have the Developer Console open, you should see two log files. The first will end in failure:

14:06:26:503 EXCEPTION_THROWN [20]|System.DmlException: Update failed. First exception on row 0 with id 0011T00002hG1FNQA0; first error: UNABLE_TO_LOCK_ROW, unable to obtain exclusive access to this record or 1 records: 0011T00002hG1FNQA0: []

While the second will succeed.

Whenever you need to test something like this, you almost certainly need to set up a real test, and Visualforce is one of the best ways to do that; Lightning Components can aggregate methods together, which might be misleading.

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