This post is dedicated to learning Salesforce triggers with examples and scenarios by dissecting them line by line. All triggers will be written with plenty of comments and explanations so that its easier for us to understand and implement.

• Write Your First Hello World Salesforce Apex Trigger – Triggers for Beginners

The “Hello World” program is the simplest program used to illustrate the basic syntax of a programming language. The program outputs “Hello World” and is traditionally the first program written by all beginner developers. Our Hello World trigger’s requirement is: When a Lead is updated, update the lead’s first name to ‘Hello’ and the last name to ‘World’

• Trigger to Change the Stage when an Opportunity is created

Every time an Opportunity is created (and the user selects any Stage), the Opportunity Stage should change and default to Prospecting.

• Trigger to create a task when an Opportunity is updated

When an Opportunity is updated, a new Task should be created and assigned to the Opportunity Owner. The status of the task should be “In Progress”

• Trigger to create a roll-up summary of Contact’s fields on Accounts

On each Account, the Total Salary custom field should hold the sum of Salaries from its associated Contacts. The trigger should work whenever a Contact’s Salary is updated, New Contact is Created or when an existing Contact is deleted.

• Trigger to Prevent Duplicate Contacts

When a Contact is being created and if a record with the same Email Id or Phone number exists, the trigger should throw an error and the User should not be allowed to create the Duplicate Contact

• Trigger to Post Automated Random Chatter Comment

When a user posts to chatter and if the user’s post contains the term “Success”, an automated comment should be posted. This comment should be randomly selected from a list of comments; And should be posted as a specific user.

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Requirement: Write a Salesforce Apex Trigger to create a Task when an Opportunity is updated. The task should be assigned to the Opportunity owner and the status of the task should be “In Progress”.

The Salesforce Apex Trigger Sytax is as follows:

trigger *triggerName* on *Object* (*before/after event*) {
    for (*Object* *Variable* : Trigger.New)      
        **Trigger Actions & Code Block**
}

Now lets write our trigger with the following steps.

1.  Define the trigger
2.  Iterate through each opportunity
3.  Create a Task
4.  Assign values to the Task

trigger createTaskOnOpp on Opportunity (before update) {

for (Opportunity Opp :Trigger.New) {

Task t = new Task();

	t.WhatID = Opp.Id;
	t.Ownerid = opp.Ownerid;
	t.subject = 'This is the Subject';
	t.Status = 'In Progress';
	t.Description = 'This is the Description';
	insert t;
	}
}

The complete Salesforce Apex Trigger to create a Task when an Opportunity is updated would be:

////define the trigger name, object and events
trigger createTaskOnOpp on Opportunity (before update) {
    //Iterate through each opportunity and assign it the variable Opp
    for (Opportunity Opp :Trigger.New) {
	//Create a new task and assign it the variable t
        Task t = new Task();
        // Assign Values to the task t
        t.WhatID          = Opp.Id;
        t.Ownerid         = opp.Ownerid;
        t.subject 	  = 'This is the Subject';
        t.Status	  = 'In Progress';
        t.Description     = 'This is the Description';
        insert t;
    }
}

This is how the trigger looks in the developer console (image)

The “Hello World” program is the simplest program used to illustrate the basic syntax of a programming language. The program outputs “Hello World” and is traditionally the first program written by all beginner developers.

Let’s write our first “Hello World” Salesforce Apex trigger which will update a Lead with “Hello” as the first name and “World” as the last name.

Requirement:
When a Lead is updated, update the lead’s first name to ‘Hello’ and last name to ‘World’

Lets write the trigger in the “Developer Console”. To access the developer console, click the drop down on your Name (on the top right), and then click on Developer Console.

Once the developer console is open, click on File >> Open >> Apex Trigger. Now we are ready to write our first trigger.

The Trigger Syntax:
Every trigger is defined by using the following syntax:

  trigger *triggerName* on *Object* (*before/after event*) {
       for (*Object* *Variable* : Trigger.New)
       **Trigger Actions & Code Block**
  }

Here is what the terms in the syntax mean:

• ‘triggerName’ is the name of the trigger which describes it.
• ‘Object’ is the name of the Object on which the trigger is created
• ‘before/after event’ are a comma separated list of events like insert, update, delete
• ‘Trigger.New’ is a list of sObject records
• ‘Variable’ denote a piece of memory that can contain a data value. Descriptive text is used as variables.

Lets get back to our requirement and based on the above syntax, write our ‘Hello World’ Salesforce Apex trigger.
Remember, when a Lead is updated, the first name should be updated to “Hello” and the Last Name to “World“.

We will be using comments to describe the lines of code in our trigger. But what are comments? Comments are used to describe code and are ignored by the parser – meaning the comments are NOT treated as code and will not run.
Single line comments are preceded by // and multi line comments are wrapped in /* and */

Now here comes the trigger:

// Name of the trigger is HelloWorld, It is on the Lead Object and It will run before the lead is updated (event).
trigger HelloWorld on Lead (before update) {
        //for every lead record, denoted by variable ld,in the list that is being updated
        for (lead ld : Trigger.new) {
             // add the first name as 'Hello'
             ld.FirstName = 'Hello';
             // add the last name as 'World'
             ld.LastName = 'World';
         }
}

This is how it looks in the developer console.

Exercise to get used to the syntax and the basic trigger for beginners:

Write a trigger to update the first name of the contact as Taha and the last name as Syed and the Phone number as 000-111-9999

The requirement is:

When a Contact is being created, if a record with the same Email or Phone number exists, the trigger should throw an error and the user should not be allowed to create the duplicate Contact.

To achieve this, we will write a trigger with the following flow:

1. Define the Trigger
2. Create Sets to store the ‘Email Ids’ and ‘Phone Numbers’ of all the records that are being created
3. Iterate through each record that is being created, and add their ‘Email Ids’ and ‘Phone Numbers’ to the Sets.
4. Create a List to store the ‘Email Ids’ and ‘Phone Numbers’ of existing records that match the records being created.
5. Populate the above List with of existing records whose email id or phone number matches the ones being created.
6. Iterate through each record being created and display and error if the record already exists.

Now lets go through each step once again and write its respective code.

trigger PreventDuplicateContacts on Contact (before insert) {

}

Set <String> emailSet = new Set<String>();
Set <String> phoneSet = new Set<String>();

for (contact con:trigger.new) {
     emailSet.add(con.email);
     phoneSet.add(con.phone);
}

// New list to store the found email or phone numbers
List <Contact> contactList = new List<Contact>();

contactList = [SELECT email,phone FROM Contact WHERE email IN :emailSet OR phone IN :phoneSet];

for (contact con:trigger.new) {
     If(contactList.size() > 0) {
     con.email.adderror( 'Duplicate Contact Found. Use Existing Contact.' ); // Displaying the error
     }
}

The complete trigger to prevent duplicate contacts by matching email or phone number and displaying the error on the email field would be:

trigger PreventDuplicateContacts on Contact (before insert) {
    
    // Set to store email ids
    Set <String> emailSet = new Set<String>(); 
    // Set to store phone numbers
    Set <String> phoneSet = new Set<String>(); 
    
    // Iterate through each Contact and add their email and phone number to their respective Sets
    for (contact con:trigger.new) {
        emailSet.add(con.email);
        phoneSet.add(con.phone);
    }

    // New list to store the found email or phone numbers
    List <Contact> contactList = new List<Contact>();

    // Populating the list using SOQL
    contactlist = [SELECT email,phone FROM Contact WHERE email IN :emailSet OR phone IN :phoneSet];

    // Iterating through each Contact record to see if the same email or phone was found
    for (contact con:trigger.new) {
        If (contactList.size() > 0) {
            // Displaying the error
            con.email.adderror( 'Duplicate Contact Found. Use Existing Contact.' );
        }
    }

}

Here is how the Trigger to Prevent Duplicate Contacts looks in the Salesforce Developer Console (image)