Debug your code with System.debug!

Preface: this post is part of the Advanced Apex Concepts series.

Let’s do a little bit of role-play! No, not that kind of role-play! And definitely not this kind!

You – the perfect student!
You’re a tenacious learner and you’ve gone through all the chapters of Sfdc99 and their quizzes.
You’re motivated to learn Apex and you’ve even started attempting some triggers all on your own!

Me – the loving but not always helpful teacher!
My mom tells me I was more handsome when I was younger.

The problem: You’re writing some code and it doesn’t work. You don’t really know anyone who can help, and even though I’m a fine gentleman, my advice hasn’t been helpful. You’ve tried Googling for answers, pretending the inside of your brain is a computer – but no luck! What do you do now?

Good news! The answers to your problems exists, and it’s called System.debug!
System.debug(‘I am awesome!’);

System.debug() simply “prints” the value of anything you put inside it!

trigger CountFriends on Contact(before insert) {
  for (Contact c : Trigger.new) {
    // We often use System.debug to see the values of variables
    System.debug('David has a new friend!');
    System.debug('Hi ' + c.FirstName + ' ' + c.LastName + '!');
  }
  List<Contact> total = [SELECT Id FROM Contact];
  System.debug('David has ' + total.size() + ' friends total.');
}

To see the output of your System.debug, you need to:

1. Write your trigger (no need for a test class yet!)
2. Open up the Developer Console:
   – Click Your Name >> Developer Console on the top right of any Salesforce page
   – You must have the “View All Data” permission to access this!
3. Do something in Salesforce that will make your trigger run!
4. Open the log for your latest action, then filter to show “Debug Only”

Here’s what the above steps will look like with our example:

How exactly does System.debug help you troubleshoot your code?
Simple! At the very minimum, System.debug will tell you where your code is breaking. For example, you can track the value of a variable with multiple System.debugs and see where it’s no longer what you expect. Most of the time, knowing where your code breaks is enough to show you how to fix it. If not, you now have a tangible reference point to begin your Google search for a solution!

Don’t be afraid to use System.debug often in your triggers!

Next post: Comparing old and new values in a trigger!