Apex Developer Guide

Apex Developer Guide
Release Notes
Getting Started with Apex
Introducing Apex
Apex Development Process
Apex Quick Start
Create a Custom Object
Add an Apex Class
Add an Apex Trigger
Add a Test Class
Deploy Components to Production
Writing Apex
Running Apex
Debugging, Testing, and Deploying Apex
Apex Reference
Appendices
PDF

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Add an Apex Trigger

In this step, you create a trigger for the Book__c custom object that calls the applyDiscount method of the MyHelloWorld class that you created in the previous step.
Prerequisites:
  • A Salesforce account in a sandbox Professional, Enterprise, Performance, or Unlimited Edition org, or an account in a Developer org.
  • The MyHelloWorld Apex class.

A trigger is a piece of code that executes before or after records of a particular type are inserted, updated, or deleted from the Lightning Platform database. Every trigger runs with a set of context variables that provide access to the records that caused the trigger to fire. All triggers run in bulk; that is, they process several records at once.

  1. From the object management settings for books, go to Triggers, and then click New.
  2. In the trigger editor, delete the default template code and enter this trigger definition: 
    1trigger HelloWorldTrigger on Book__c (before insert) {
2
3   Book__c[] books = Trigger.new;
4
5   MyHelloWorld.applyDiscount(books);
6}

    The first line of code defines the trigger:

    1trigger HelloWorldTrigger on Book__c (before insert) {

    It gives the trigger a name, specifies the object on which it operates, and defines the events that cause it to fire. For example, this trigger is called HelloWorldTrigger, it operates on the Book__c object, and runs before new books are inserted into the database.

    The next line in the trigger creates a list of book records named books and assigns it the contents of a trigger context variable called Trigger.new. Trigger context variables such as Trigger.new are implicitly defined in all triggers and provide access to the records that caused the trigger to fire. In this case, Trigger.new contains all the new books that are about to be inserted.

    1Book__c[] books = Trigger.new;

    The next line in the code calls the method applyDiscount in the MyHelloWorld class. It passes in the array of new books. 

    1MyHelloWorld.applyDiscount(books);
You now have all the code that is needed to update the price of all books that get inserted. However, there’s still one piece of the puzzle missing. Unit tests are an important part of writing code and are required. In the next step, you'll see why this is so and will be able to add a test class.