Fire Trigger on Field Change

Question

I am trying to create a trigger that will fire only when the Probability % (Probability) is changed over 10% and update the contact roles (contact) with a date of this event happening (SQLDate__c). The trigger is currently firing on any change of the opportunity.

How can this be changed to fire only on the Probability % going above 10% (if it falls below I don't need any change to happen).

Thanks!!

trigger UpdateContact on Opportunity (after insert, after update) {

    OpportunityContactRole ocr;
    Contact contact;
    Opportunity opp = Trigger.new[0];
    list<Contact> listToUpdate = new list<Contact>();
    if(opp.Probability > 10)
    {

        for(OpportunityContactRole iterating_oppConRole : [SELECT o.Role, 
                                                                  o.OpportunityId, 
                                                                  o.IsPrimary, 
                                                                  o.Id, 
                                                                  o.ContactId,
                                                                  o.Contact.SQLDate__c 
         FROM OpportunityContactRole o where o.OpportunityId =: opp.id])
      {

            Contact tempContact = new Contact(id=iterating_oppConRole.ContactId, SQLDate__c = system.today());
            listToUpdate.add(tempContact);

       }
    }
        if(!listToUpdate.isEmpty())
        update listToUpdate;
}

Answer 1

More filtering is possible because both the old and new value of fields are available in the Trigger Context. So you should use code like this to minimise the updates:

Set<Id> oppIds = new Set<Id>();
for (Opportunity opp : Trigger.new) {
    Opportunity old = Trigger.oldMap.get(opp.Id);
    if (opp.Probability != old.Probability) {
        if (opp.Probability > 10) {
            oppIds.add(opp.Id);
        }
    }
}
if (oppIds.size() > 0) {
    // Use a Map to avoid duplicates
    Map<Id, Contact> updates = new Map<Id, Contact>();
    for(OpportunityContactRole ocr : [
            select ContactId
            from OpportunityContactRole
            where o.OpportunityId in :oppIds
            and ContactId != null
            } {
        updates.put(ocr.ContactId, new Contact(
                Id = ocr.Contact,
                SQLDate__c = Date.today()
                ));
    }
    update updates.values();
}

This code is bulkified too.

Answer 2

You're doing as much as you can currently. There is no more granular firing mechanism than before/after update/insert. All you can do is filter out the records which don't match your criteria, as you are in your code. Be aware though, as previously mentioned, currently your code is not properly bulkified.