WHAT IS AFTER UPDATE EVENT IN APEX TRIGGER, EXPLAIN IT WITH AN EXAMPLE?

AFTER UPDATE:

This event runs the block of code after the updated data is committed to the database. Operations such as creating or updating related records can be performed under this event.

SYNTAX:

trigger triggerName on objectName (after update) {

   // Block of code

}

SCENARIO:

We are having the requirement that when an account record is updated, we need to update all related contact record phone number field with the Account phone number.

APEX TRIGGER:

trigger AccountMainTrigger on Account (after update) {

    if (Trigger.isAfter && Trigger.isUpdate) {

        updateContactClass obj = new updateContactClass ();

        obj.updateContactPhones(Trigger.new); // Calling method to update contacts after account update

    }

}

APEX CLASS:

public class updateContactClass {

    

    public void updateContactPhones(List<Account> accountList) {

        Set<Id> accountIdSet = new Set<Id>();

        List<Contact> conList = new List<Contact>();

        // Collecting account IDs to query related contacts

        for (Account acc : accountList) {

            accountIdSet.add(acc.Id); // Add account Ids to the set

        }

        // Querying accounts with their related contacts in bulk

        List<Account> accountsWithContacts = [SELECT Id, Phone, (SELECT Id, Phone FROM Contacts) 

                                               FROM Account 

                                               WHERE Id IN :accountIdSet];

        // Prepare a map to store accountId -> Phone number

        Map<Id, String> accountPhoneMap = new Map<Id, String>();

        for (Account acc : accountsWithContacts) {

            // Map the account ID to its phone number

            accountPhoneMap.put(acc.Id, acc.Phone);

        }

        // Now process the contacts in bulk without nested loops

        for (Contact con : [SELECT Id, Phone, AccountId FROM Contact WHERE AccountId IN :accountIdSet]) {

            // If the contact's AccountId exists in the map, update the contact's phone

            if (accountPhoneMap.containsKey(con.AccountId)) {

                con.Phone = accountPhoneMap.get(con.AccountId); // Update contact phone

                conList.add(con); // Add to the list for bulk DML operation

            }

        }

        // Performing the update operation only if there are contacts to update

        if (!conList.isEmpty()) {

            try {

                update conList; // Bulk DML update

            } catch (DmlException e) {

                // Handle DML exception if needed (e.g., logging the error)

                System.debug('Error during update: ' + e.getMessage());

            }

        }

    }

}

Now let us update the phone number on account record to see the results,

Before updating  the Account record,

After updating the Account record with different phone number,