Your First Trigger

A sales team wants every new Opportunity with an Amount over R100,000 automatically flagged as high-priority by setting a custom Priority__c field to 'High' — without a sales rep needing to remember to set it manually every time.

trigger OpportunityTrigger on Opportunity (before insert) {
    for (Opportunity opp : Trigger.new) {
        if (opp.Amount != null && opp.Amount > 100000) {
            opp.Priority__c = 'High';
        }
    }
}

1. trigger OpportunityTrigger on Opportunity (before insert) { — before insert (Lesson 2 — modifying a field, so it must run before the save).
2. for (Opportunity opp : Trigger.new) { — Trigger.new (Lesson 3 — the records being inserted).
3. if (opp.Amount != null && opp.Amount > 100000) { — a plain if statement (Module 6) applying the actual business rule.
4. opp.Priority__c = 'High'; — flags high-value deals automatically.
5. } — closes the if.
6. } — closes the loop.
7. } — closes the trigger.

Opportunity opp = new Opportunity(Name = 'Big Deal', Amount = 150000, StageName = 'Prospecting', CloseDate = Date.today());
insert opp;

System.debug(opp.Priority__c); // 'High'

1. Opportunity opp = new Opportunity(Name = 'Big Deal', Amount = 150000, StageName = 'Prospecting', CloseDate = Date.today()); — a new opportunity, Amount well over the threshold.
2. insert opp; — triggers OpportunityTrigger automatically; inside it, Trigger.new contains opp; opp.Amount (150000) is greater than 100000, so Priority__c gets set to 'High' before the actual save.
3. (blank line)
4. System.debug(opp.Priority__c); — logs 'High' — the inserted record ends up with Priority__c already correctly populated, with zero extra code required at the call site.