Episode 5 – Demystifying Apex Triggers

In this post we will learn about writing triggers in Salesforce to fire business logic using Apex. Apex triggers within Salesforce are designed to help you automate certain tasks. Apex triggers allow you to perform custom actions before and after events in Salesforce. These events can include things such as data insertions, updates to existing data, or deletions.

What is Apex Trigger in Salesforce?

Trigger is a procedure in database which automatically invokes whenever a special events in Database occurs. Apex triggers enable you to perform custom actions before or after events to records in Salesforce, such as insertions, updates, or deletions.

What is Apex Trigger in Salesforce?
Apex Triggers

When Should we Use Trigger?

There lots of automation tool available in Salesforce. Lets understand the when to use Apex Trigger in Salesforce.

  1. Complex logic incapable of being processed via declarative artifacts
  2. Logic associated with DML
  3. Operations on unrelated objects
  4. Integration with External Systems

What are different type of Triggers?

There are two types of triggers in Salesforce.

  • Before triggers are used to perform a task before a record is inserted or updated or deleted in Salesforce. These are used to update or validate record values before they are saved to the database.
  • After triggers are used if we want to use the information set by Salesforce system and to make changes in the other records. The records that fire the after trigger are read-only.

Trigger Events in Salesforce

A trigger is a set of statement which can be executed on the following events. We can add below events with comma-separated. Here is a list of trigger events in salesforce.

Trigger Events in Salesforce

Trigger Context Variable

All triggers define implicit variables that allow developers to access run-time context. These variables are contained in the System.Trigger class

Variable Usage
isExecuting It tells if code current context is trigger or not
isInsert It returns true if trigger fires on insert operation
isUpdate It returns true if trigger fires on update operation
isDelete It returns true if trigger fires on delete operation
isBefore It returns true if code is running in Before context
isAfter It returns true if code is running in After context
new It holds list of new versions of sObject records This sObject list is only available in insert, update, and undelete triggers, and the records can only be modified in before triggers
newMap It holds new versions of sObject in key value pair This map is only available in before update, after insert, after update, and after undelete triggers
old It holds list of old versions of sObject records This sObject list is only available in update and delete triggers
oldMap It holds old versions of sObject in key value pair This map is only available in update and delete triggers.
operationType Returns an enum of type System.TriggerOperation corresponding to the current operation. System.TriggerOperation enum are: BEFORE_INSERT, BEFORE_UPDATE, BEFORE_DELETE,AFTER_INSERT, AFTER_UPDATE, AFTER_DELETE, and AFTER_UNDELETE
size The total number of records in a trigger invocation, both old and new.

Example of Apex Trigger

Demo 1 : Using context variable in Trigger

Let see the first demo of context variable in Trigger.

trigger AccountTrigger on Account (before insert, before update, after update) {
    if(Trigger.isBefore && Trigger.isInsert){
        System.debug('I am in AccountTrigger before insert context');
            for(Account acc :Trigger.new){
                System.debug('New Name'+ acc.Name);
                System.debug('Old Name'+ Trigger.oldMap.get(acc.Id).Name);


Check our our recording for the session.

Trigger Handler pattern

Check this blog post to learn about which all trigger pattern are available in Salesforce. For Trigger Handler code check this post.

Trigger Handler pattern
Trigger Handler Pattern

Check below ode how to write trigger handler pattern.

Create one Trigger “AccountTrigger

trigger AccountTrigger on Account( after insert, after update, before insert, before update){
    AccountTriggerHandler handler = new AccountTriggerHandler(Trigger.isExecuting, Trigger.size);   
    if( Trigger.isInsert ){
    else if ( Trigger.isUpdate ){
        if(Trigger.isBefore){ handler.OnBeforeUpdate(trigger.New,trigger.Old,Trigger.NewMap,Trigger.OldMap);

Create one Trigger Handler Class

public with sharing class AccountTriggerHandler 
    private boolean m_isExecuting = false;
    private integer BatchSize = 0;
    public static boolean IsFromBachJob ;
    public static boolean isFromUploadAPI=false;
    public AccountTriggerHandler(boolean isExecuting, integer size){
        m_isExecuting = isExecuting;
        BatchSize = size;

    public void OnBeforeInsert(List<Account> newAccount){
        system.debug('Account Trigger On Before Insert');
    public void OnAfterInsert(List<Account> newAccount){
        system.debug('Account Trigger On After Insert');
    public void OnAfterUpdate( List<Account> newAccount, List<Account> oldAccount, Map<ID, Account> newAccountMap , Map<ID, Account> oldAccountMap ){
        system.debug('Account Trigger On After Update ');
        AccountActions.updateContact (newAccount);
    public void OnBeforeUpdate( List<Account> newAccount, List<Account> oldAccount, Map<ID, Account> newAccountMap , Map<ID, Account> oldAccountMap ){
        system.debug('Account Trigger On Before Update ');

    public static void OnAfterUpdateAsync(Set<ID> newAccountIDs){
    public boolean IsTriggerContext{
        get{ return m_isExecuting;}
    public boolean IsVisualforcePageContext{
        get{ return !IsTriggerContext;}
    public boolean IsWebServiceContext{
        get{ return !IsTriggerContext;}
    public boolean IsExecuteAnonymousContext{
        get{ return !IsTriggerContext;}

Create one Trigger Action Class

public without sharing class AccountActions{
    public static void updateContact ( List<Account> newAccount){   
        // Add your logic here

Trigger Best Practice

  1. One Trigger Per Object : A single Apex Trigger is all you need for one particular object. If you develop multiple Triggers for a single object, you have no way of controlling the order of execution if those Triggers can run in the same contexts
  2. Logic-less Triggers : If you write methods in your Triggers, those can’t be exposed for test purposes. You also can’t expose logic to be re-used anywhere else in your org.
  3. Context-Specific Handler Methods : Create context-specific handler methods in Trigger handlers
  4. Bulkify your Code : Bulkifying Apex code refers to the concept of making sure the code properly handles more than one record at a time.
  5. Avoid SOQL Queries or DML statements inside FOR Loops : An individual Apex request gets a maximum of 100 SOQL queries before exceeding that governor limit. So if this trigger is invoked by a batch of more than 100 Account records, the governor limit will throw a runtime exception.
  6. Using Collections, Streamlining Queries, and Efficient For Loops : It is important to use Apex Collections to efficiently query data and store the data in memory. A combination of using collections and streamlining SOQL queries can substantially help writing efficient Apex code and avoid governor limits.
  7. Querying Large Data Sets : The total number of records that can be returned by SOQL queries in a request is 50,000. If returning a large set of queries causes you to exceed your heap limit, then a SOQL query for loop must be used instead. It can process multiple batches of records through the use of internal calls to query and queryMore
  8. Use @future Appropriately : It is critical to write your Apex code to efficiently handle bulk or many records at a time. This is also true for asynchronous Apex methods (those annotated with the @future keyword). The differences between synchronous and asynchronous Apex can be found
  9. Avoid Hardcoding IDs : When deploying Apex code between sandbox and production environments, or installing Force.com AppExchange packages, it is essential to avoid hardcoding IDs in the Apex code. By doing so, if the record IDs change between environments, the logic can dynamically identify the proper data to operate against and not fail

Trigger Order of Execution

Here is recording of our old session on Order of Execution. Check this blog post to learn more.

Always remember below points before writing trigger :-
1) Order Of Execution
2) Learn about Other Trigger Framework


Create Custom object Invoice with field Total Amount
Create child object Invoice Line Item with Lookup relationship to Invoice.
Add price field into Invoice Line Item.
Write trigger on Invoice Line Item which will add some of all child records to parent Invoice

Further Learning

Trigger Framework

Learn how to completely and cleanly control your Apex code with Trigger Frameworks, why they’re useful, and the various ways to implement them. In this session will talk about Apex Trigger Framework in Salesforce and benefit of using a trigger framework, How many trigger framework are available, which one is lightweight apex trigger framework and Comparison of different approaches.

Don’t forget to register for our next session on Test Classes. Check this post for all other session detail.

Make sure to subscribe our YouTube channel to get notification for video upload. So, learn at your pace and free will and ace your journey to Salesforce!


I hope this post helped you to understand the Triggers in Salesforce and Best practices of Apex triggers. We tried to covered all about triggers in Apex including type of triggers, Handler pattern and different Triggers frameworks available in market.


  1. Reply
    Ankit Desai says:

    Completed Assignment for Day 5
    I have created one trigger “InvoiceAmountUpdate” and one class “InvoiceAmountUpdateHandler”

  2. Reply
    Aathirai says:

    Completed Day 5 Assignment

  3. Reply
    A Belano says:

    Day 5 Assignment Completed

  4. Reply
    Brisilda says:

    Episode 5 – Demystifying Apex Triggers Assignment Completed!

  5. Reply
    Archit Dutt Sharma says:

    Completed Day 5 assignment

  6. Reply
    Anuj Sahu says:

    Day 5 Assignment is completed

  7. Reply
    Marishell Cruz says:


    • Reply
      Amit Chaudhary says:

      8 more to go

    • Reply
      Pb says:

      Can someone update all the solution?

  8. Reply
    Jaya Iyer says:

    completed assignment 5

  9. Reply
    Pb says:

    Solution plz

    • Reply
      Amit Chaudhary says:

      After contest over

  10. Reply
    Arjinder Kaur says:

    assignment 5 completed

  11. Reply
    Pritam Pramod Dalvi says:

    Assignment 5 Completed

  12. Reply

    Day 5 Assignment is completed

  13. Reply

    Day 5 Assignment is completed

  14. Reply
    Arjinder Kaur says:

    Solution for Assignment : Trigger on Invoice Line Item which will add sum of all child records to parent Invoice:

    trigger AddInvoiceItems on Invoice_Line_Item__c ( after insert, after update, after delete ) {

    List ListIds = new List();

    if ( Trigger.isInsert || Trigger.isUpdate ) {

    for ( Invoice_Line_Item__c item : Trigger.New ) {
    if ( Trigger.isInsert || ( Trigger.isUpdate && Trigger.OldMap.get(item.ID).price__c!=item.price__c) ) {



    for( Invoice_Line_Item__c item : Trigger.Old ) {



    Map TotalPriceMap = new Map();

    for ( Invoice_Line_Item__c item : [ SELECT Id, price__c, invoice__c FROM Invoice_Line_Item__c WHERE invoice__c IN : ListIds ] ) {

    Decimal totalPrice = 0;
    if( TotalPriceMap.containsKey ( item.invoice__c ) )
    totalPrice = TotalPriceMap.get( item.invoice__c );
    totalPrice = totalPrice + item.price__c;

    List updateInvoice = new List();
    for ( Id invoiceId : TotalPriceMap.KeySet() ) {
    Invoice__c inv = new Invoice__c ( Id = invoiceId );
    inv.Total_Amount__c = TotalPriceMap.get( invoiceId );

    if ( updateInvoice.size() > 0 )
    Update updateInvoice;


    • Reply
      kishore goud says:

      HI bro, i have one question, you have declared empty map . since it is empty how you are searching using containskey

      • Reply
        Arjinder Kaur says:

        Thanks for pointing out. It should be like this:

        Map TotalPriceMap = new Map();

        I believe, datatype got missed while I pasted my solution.
        I am sorry about it. I will check and correct it.

        Thanks again!

    • Reply
      Arjinder Kaur says:

      Corrections to the code – Please check comments below

  15. Reply
    kishore goud says:

    HI bro, i have one question, you have declared empty map . since it is empty how you are searching using containskey

    • Reply
      Arjinder Kaur says:

      Facing some issue with code within angle brackets after I posted comment.

      List ListIds = new List(); // Id within angle brackets after List
      Map TotalPriceMap = new Map(); // Id,Decimal within angle brackets after Map
      List updateInvoice = new List(); // Invoice__c within angle brackets after List

  16. Reply
    Arjinder Kaur says:

    Noticed some issues with posted code : I noticed code(data type) within angle brackets got removed after I posted it. I am sorry about this.
    Please add following datatype ( written after backslash ) within angle bracket after List or Map


    List ListIds = new List(); // Add Id within angle brackets after List

    Map TotalPriceMap = new Map(); // Add Id , Decimal within angle brackets after Map

    List updateInvoice = new List(); // Add Invoice__c within angle brackets after List

  17. Reply
    Ankit Desai says:

    Code for Assignment Day 5

    trigger InvoiceAmountUpdate on Invoice_Line_Item__c (after insert,
    after update,
    after delete) {

    String invoiceId = ”;
    if(Trigger.isInsert || Trigger.isUpdate) {
    for(Invoice_Line_Item__c invoiceLineItem : Trigger.new) {
    if(invoiceLineItem.Invoice__c != null) {
    invoiceId = invoiceLineItem.Invoice__c;
    for(Invoice_Line_Item__c invoiceLineItem : Trigger.old) {
    if(invoiceLineItem.Invoice__c != null) {
    invoiceId = invoiceLineItem.Invoice__c;
    if(invoiceId != ”) {


    public class InvoiceAmountUpdateHandler {
    public static void updateInvoiceAmount(String invoiceId) {
    List items = new List();
    items = [select Id,price__c from Invoice_Line_Item__c where Invoice__c = :invoiceId];
    Decimal amount = 0;
    for(Invoice_Line_Item__c item : items) {
    amount = amount + item.Price__c;
    Invoice__c invoice = new Invoice__c();
    invoice.Id = invoiceId;
    invoice.Total_Amount__c = amount;
    update invoice;


    • Reply
      swathi says:

      Hi! I have written a code for trigger assignment task and its working well for insert and update. Can you please tell me whether I need to modify my code for better results..

      Parent: Invoice__c
      Child: Invoice_Line_Item__c

      Trigger code:
      trigger Invoice_Line_Item__cTrigger on Invoice_Line_Item__c (after insert, after Update) {

      if((trigger.IsInsert == true && Trigger.Isafter == true) ||(trigger.IsUpdate == true && Trigger.Isafter == true)){



      public class Invoice_Line_ItemHandler {

      public static list P_id = new list();
      public static decimal amount=0;

      public static void AmoutUpd(list ChildRec){

      for(Student__c Pid : StuRec){

      if(pid.Teacher_name__c != null){

      list Rec = [SELECT Total_amout__c,name,(SELECT Invoice_name__c,price__c FROM Invoice_Line_Item__r) FROM Invoice__c WHERE ID IN :P_id];

      for(Invoice__c a: Rec){

      for(Invoice_Line_Item__c b: a.Invoice_Line_Item__r){

      amount = amount+ b.price__c ;

      a.Total_amout__c = amount;
      update Rec;


    • Reply
      sapna says:

      Hey, if we want to delete some record from Invoice line item and again add the record in Invoice line item and i have created one more filed at Invoice line item that is count of line Item in particular Invoice then count should be increase… how to do it??

  18. Reply
    Jim says:

    I copied the Handler Class from above into the Dev console but I receive Unexpected token ‘List’. error for this statement:
    List items = new List();

    What am i missing here?


  19. Reply
    Kiran says:

    Logic for Trigger
    public class ApexHourTriggerAssignment {

    public static void updateInvoceObjectField(List lstinvln){
    Decimal amount=0;
    Set liStIds = new Set();
    for (Invoice_Line_Up__c ilu :lstinvln) {
    if(ilu.Invoice_Name__c != null) {
    List ListInvoice = [Select id, Total_Amount__c, (select id, price__c from Invoices_Line_up__r)
    from Invoice__c Where Id IN :liStIds];
    ListListInv = new List();
    For(Invoice__c inv : ListInvoice){
    for(Invoice_Line_Up__c ilu1 : inv.Invoices_Line_up__r){
    amount = amount + ilu1.price__c;
    inv.Total_Amount__c = amount;
    update ListInv;

    trigger ApexHourTriggerAssignmentTrigger on Invoice_Line_Up__c (After insert,After Update) {


  20. Reply
    Sagar says:

    My solution for assignment.

    trigger TotalInvoiceAmount on Invoice_Line_Item__c (after insert) {

    Map UniqueInvoiceToUpdate = new map(); // To maintain unique sobject to be updated
    Map TotalAMount = new Map(); // To maintain the updated amount of each invoice sobject

    ListInvoiceToUpdate = new List(); // final list to perform dml update operation
    Invoice__c ParentInvoice;

    for (Invoice_Line_Item__c currentInvoiceItem : Trigger.New) {

    ParentInvoice = [select id, Total_Amount__c from Invoice__c where Id = :currentInvoiceItem.Invoice__c LIMIT 1][0];

    // Check if we have updated total value of invoice in previous iterations:
    if (TotalAmount.get(ParentInvoice.Id) != null) {

    // if yes, add the current amount of invoice line item to the previous updated invoice object.
    // Not that, we have not commit to database yet. Hence we are retrieving updated amount from map and not from sobject’s Total amount field
    ParentInvoice.Total_Amount__c = TotalAmount.get(ParentInvoice.Id) + currentInvoiceItem.Amount__c;
    else {
    // We haven’t saved total amount in map yet.
    // Add current invoice line item amount to total amount of invoice object.
    ParentInvoice.Total_Amount__c += currentInvoiceItem.Amount__c;
    // save updated total amount of invoice object in map
    TotalAmount.put(ParentInvoice.Id, ParentInvoice.Total_Amount__c );

    // update invoice object’s map.
    UniqueInvoiceToUpdate.put(ParentInvoice.Id, ParentInvoice);

    // iterate UniqueInvoiceToUpdate map to put those invoice objects in list.
    for (Invoice__c I : UniqueInvoiceToUpdate.values()){

    // update list.
    update InvoiceToUpdate;

    Any better solution?

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