Before and After Triggers
By the end of this lesson, you'll be able to:
- Distinguish a before trigger from an after trigger
- Choose the correct trigger timing for a given task
- Explain why modifying a field only works correctly in a before trigger
Prerequisites: "What Is a Trigger?"
before: modify the record on its way in
trigger AccountTrigger on Account (before insert) {
for (Account acc : Trigger.new) {
if (String.isBlank(acc.Industry)) {
acc.Industry = 'Unknown';
}
}
}A before insert trigger runs before the record is actually saved — this is exactly Module 19's "What Really Happens When You Insert a Record" sequence, step 2. Changing a field here (like defaulting a blank Industry) becomes part of what actually gets saved, with no extra update DML needed.
after: react once the record is permanent
trigger AccountTrigger on Account (after insert) {
for (Account acc : Trigger.new) {
System.debug('Account saved with Id: ' + acc.Id);
}
}An after insert trigger runs after the save — step 5 from Module 19's sequence — so acc.Id is already populated here. This is the right place for logic that needs the final saved state, like creating a related record that needs this Account's real Id.
Why field changes belong in before, not after
// WRONG PLACE for a field default
trigger AccountTrigger on Account (after insert) {
for (Account acc : Trigger.new) {
acc.Industry = 'Unknown'; // too late — already saved without this!
update acc; // requires an extra, avoidable DML statement
}
}By the time an after trigger runs, the record is already saved — changing a field here doesn't retroactively change what was saved; it requires an entirely separate update DML statement to apply the change. This is exactly why Industry defaulting belongs in before insert: the change becomes part of the original save, with no second DML operation needed at all.
Exercise
As a comment, decide whether defaulting a blank Rating field to 'Cold' belongs in a before or after trigger, and explain why.
Show hint
Think about whether an extra DML statement would be needed.
Before and After Triggers Quiz
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Summary
before triggers run prior to the actual save and can still modify the record being saved; after triggers run once the save is complete and can see the final, permanent state — including the Id.