New to Apex- only updating specific records

Question

I am new to Apex coding and trying to build a simple trigger that connects online activity to a checkbox on opportunities. We have a custom object (Online_Activity__c) where records are created automatically by an external system. We'd like a certain online activity to cause a checkbox on the opportunity to go from false to true. However, we only want the checkbox on a certain opportunity to be checked. My code is below-

trigger purlOpp on Online_Activity__c (after insert) {
  for (Online_Activity__c updatePurlOpp : Trigger.new) {
    if (updatePurlOpp.Description__c.startswith ('2015 PURL Page Visit')) {
       updatePurlOpp.What__r.Opportunity.PurlLink = true;
      }
   }
}

My question is where can I add the criteria to only update the opportunity checkbox on opportunities where Year__c = 2015 (picklist value) and Value_Prop__c = "External Product Renewal" (string). The what__r is the account object api name on Online Activity.

Answer 1

Its fairly straightforward to get you there.

The Code

trigger updateRelatedOppty on Online_Activity__c (after insert) {

    Set<String> oIDs = new Set<String>();
    List<Opportunity> oList = new List<Opportunity>();

    //grab the IDs of the Opptys you want to update
    for(List<Online_Activity__c> tmpList : [SELECT Id, Opportunity__c 
                                            FROM Online_Activity__c 
                                            WHERE Id IN :Trigger.New])
    {
        for(Online_Activity__c tmp : tmpList) {
            oIDs.add(tmp.Opportunity__c);
        }
    }

    //populate a list of Opptys to update
    for(List<Opportunity> tmpList : [Select Id, Rad_Checkbox__c, Year__c, Value_Prop__c FROM Opportunity WHERE Id IN :oIDs AND Year__c = '2015' AND Value_Prop__c LIKE 'External Product Renewal']) {
        for(Opportunity tmp : tmpList) {
            tmp.Rad_Checkbox__c = true;
            oList.add(tmp);
        }    
    }

    //update the Opptys
    try {
        update oList;
    } catch (Exception e) {
        System.debug('Exception: ' + e);       
    }    
}

Recommended Next Steps

In no particular order of importance...
1) This is beta code. Optimize it, best-practice it.
2) Definitely pull ALL of this functionality OUT of the Trigger and into a Class. Call that Class (and other classes) from a master trigger, you only need one (1) trigger per object.
3) Make sure you understand things well enough to write a meaningful Apex unit test with truth assertions (e.g. System.AssertEquals)!
4) Order of execution across multiple Triggers (or multiple code blocks referenced in a single Trigger) can be challenging.
5) It is very important to understand Triggers and their Context Variables.

Best of luck, I hope this helps you get started!