Intermediate 25 min read

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';
        }
    }
}

trigger AccountTrigger on Account (before insert) { — 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.
for (Account acc : Trigger.new) { — loops over the records about to be inserted.
if (String.isBlank(acc.Industry)) { — checks for a blank field.
acc.Industry = 'Unknown'; — changing a field here becomes part of what actually gets saved, with no extra update DML needed.
} — closes the if.
} — closes the loop.
} — closes the trigger.

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);
    }
}

trigger AccountTrigger on Account (after insert) { — an after insert trigger runs after the save — step 5 from Module 19's sequence.
for (Account acc : Trigger.new) { — loops over the now-saved records.
System.debug('Account saved with Id: ' + acc.Id); — acc.Id is already populated here — the right place for logic that needs the final saved state.
} — closes the loop.
} — closes the trigger.

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
    }
}

// WRONG PLACE for a field default — the label says it all.
trigger AccountTrigger on Account (after insert) { — by the time an after trigger runs, the record is already saved.
for (Account acc : Trigger.new) { — loops over the saved records.
acc.Industry = 'Unknown'; — changing a field here doesn't retroactively change what was saved.
update acc; — requires an entirely separate update DML statement to apply the change.
} — closes the loop.
} — closes the trigger.

Warning: Line 5 runs update acc; inside a for loop — exactly the DML-in-a-loop governor-limit problem from Module 7 and Module 18, on top of being the wrong trigger timing. Defaulting Industry in before insert (previous section) avoids both problems at once: 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.

APEX

Before and After Triggers Quiz

1. Why is a before trigger the right place to default a blank field, rather than after?

The change becomes part of the original save, with no extra DML statement needed after triggers cannot modify fields at all, even with extra DML before triggers run faster than after triggers There is no real difference between the two

My Notes

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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.

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