Apex Trigger in Salesforce: Complete Beginner Guide with Examples

If you are learning Salesforce development, Apex Triggers are one of the first things you need to master.

Many beginners feel confused when they first see trigger code. It looks complex, but once you understand the basics, it becomes very simple.

In this guide, you will learn what Apex Triggers are, how they work, and how to write your first trigger with real examples.

What is an Apex Trigger?

An Apex Trigger is a piece of code that runs automatically before or after a record is inserted, updated, deleted, or undeleted in Salesforce.

Think of it like this:

Every time something happens to a record — a trigger can react to it automatically.

Simple example: When a new Account is created, automatically create a related Task for the owner.

When to Use Apex Trigger

Use a trigger when:

• Flow or Process Builder cannot handle the logic
• You need complex conditions or calculations
• You need to update related records automatically
• You need to validate data before saving

Trigger Syntax (Basic Structure)

java

trigger TriggerName on ObjectName (trigger events) {
    // your code here
}

Real example:

java

trigger AccountTrigger on Account (before insert, after insert) {
    // your code here
}

Types of Triggers

There are two main types:

1. Before Trigger

Runs before the record is saved to the database

Use it when:

• You want to validate or modify field values before saving
• Example: Check if phone number is empty before inserting

java

trigger AccountTrigger on Account (before insert) {
    for (Account acc : Trigger.new) {
        if (acc.Phone == null) {
            acc.Phone = '0000000000';
        }
    }
}

2. After Trigger

Runs after the record is saved to the database

Use it when:

• You want to create or update related records
• Example: Create a Task after a new Lead is inserted

java

trigger LeadTrigger on Lead (after insert) {
    List<Task> tasks = new List<Task>();
    for (Lead ld : Trigger.new) {
        Task t = new Task();
        t.Subject = 'Follow up with Lead';
        t.WhoId = ld.Id;
        tasks.add(t);
    }
    insert tasks;
}

Trigger Events

You can combine multiple events in one trigger:

Trigger Context Variables

These are special variables available inside every trigger:

Real World Example — Complete Trigger

Scenario: When an Opportunity is marked as Closed Won, automatically create a follow-up Task

java

trigger OpportunityTrigger on Opportunity (after update) {
    List<Task> tasks = new List<Task>();
    
    for (Opportunity opp : Trigger.new) {
        Opportunity oldOpp = Trigger.oldMap.get(opp.Id);
        
        if (opp.StageName == 'Closed Won' && 
            oldOpp.StageName != 'Closed Won') {
            
            Task t = new Task();
            t.Subject = 'Send thank you email to customer';
            t.WhatId = opp.Id;
            t.ActivityDate = Date.today().addDays(1);
            tasks.add(t);
        }
    }
    
    if (!tasks.isEmpty()) {
        insert tasks;
    }
}

Apex Trigger Best Practices

1. One Trigger Per Object Never create multiple triggers on the same object — it causes unpredictable behavior

2. No Logic in Trigger Keep trigger code clean — move all logic to a Handler class

java

trigger AccountTrigger on Account (before insert, after insert) {
    AccountTriggerHandler.handleBeforeInsert(Trigger.new);
}

3. Bulkify Your Code Always write code that can handle multiple records at once — never put SOQL inside a loop

❌ Wrong:

java

for (Account acc : Trigger.new) {
    List<Contact> cons = [SELECT Id FROM Contact WHERE AccountId = :acc.Id];
}

✅ Right:

java

Set<Id> accountIds = new Set<Id>();
for (Account acc : Trigger.new) {
    accountIds.add(acc.Id);
}
List<Contact> cons = [SELECT Id FROM Contact WHERE AccountId IN :accountIds];

4. Always Check for Empty Lists Before DML operations, always check if list is empty

java

if (!tasks.isEmpty()) {
    insert tasks;
}

5. Use Try-Catch for Error Handling Always handle exceptions gracefully

Common Mistakes Beginners Make

1. SOQL inside for loop This hits governor limits very quickly — always move SOQL outside loops

2. Hardcoding values Never hardcode Ids or values — use Custom Labels or Custom Settings

3. Not bulkifying code Always assume multiple records will be processed at once

4. Multiple triggers on same object Always use one trigger per object with a handler class

Apex Trigger vs Flow — When to Use What

Conclusion

Apex Triggers are a powerful tool in Salesforce development. Once you understand before vs after triggers and context variables, you can automate almost anything.

Start with simple before insert triggers, then move to after insert and after update. Practice on a free Developer org and build real examples.

The more you practice, the more confident you will become.

Found this helpful? Share it with your Salesforce learning community. Have questions? Drop them in the comments below.

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