@Jeff.,

 Hello Jeff, 

Important things to consider before we start.,

 -> Writing trigger on QQ object , while inserting ideally we wouldnt have any opportunities that were child to this QQ record so we doesnt need to handle any insert event
 -> We should query the opportunity records that were children to the QQ record that was being updated.
 -> Try the below link which explains the trigger context variables.
 https://www.salesforce.com/us/developer/docs/apexcode/Content/apex_triggers_context_variables.htm
 
 -> Trigger context variables will have the information of the records on which the trigger got fired.
 -> Ideally if the update is on cross object (any other objects record other than the trigger got fired), always go for the after trigger events
 -> Naming convention will play a major role in future, if we visit back the same code., so try to name the variables appropriatelyTotal__c

 Coming to the code., the trigger will be something like this:
 

trigger UpdateOppProb on QQ__c (after update) {
	
	Map<Id,Decimal>QQRecordMap=new Map<Id,Decimal>();//To capture the current QQ records that had any  change in total
	for(QQ__c QQRecord : Trigger.new) {
        // Verifying all possible cases of total changes that could happen than earlier
		if((trigger.oldMap.get(QQRecord.id).Total__c!=Null && QQRecord.Total__c!=Null &&trigger.oldMap.get(QQRecord.id).Total__c!=QQRecord.Total__c) || (trigger.oldMap.get(QQRecord.id).Total__c==Null && QQRecord.Total__c!=Null) || (trigger.oldMap.get(QQRecord.id).Total__c!=Null && QQRecord.Total__c==Null)){ 
			QQRecordMap.put(QQRecord.id,QQRecord.Total__c);
		}
    }//By end of this loop, the map will have all the QQ records info that we need
	
    //Now its time to query the opportunity records that need The change in probability
	
	List<Opportunity>OppsToUpdate=new List<Opportunity>();
	
	for(Opportunity OppRecord:[select id,QQ__c from Opportunity where QQ__c IN : QQRecordMap.keySet()]){
		OppsToUpdate.add(new Opportunity(id=OppRecord.id,QQRecordMap.get(OppRecord.QQ__c)));
	}// Now we prepared the list of opps that needs to get updated.
	
	if(OppsToUpdate!=Null && OppsToUpdate.size()>0){
		update OppsToUpdate;
	}
}

In the preivous trigger we queried the QQ information, where as in the current one we have the QQ information in our hand, we need to query all the opportunities that were tied to this guy as children and update them.



A small change in previous trigger,

trigger TestUpdateProbability on Opportunity (before insert, before update) {
		
		Set<Id>QQIdset=new Set<Id>();//to collect the qq ids that we need
		
        for(Opportunity p : Trigger.new) {
                
				QQIdset.add(p.QQ__c);
        }
		Map<Id,QQ__c>QQRecordMap=new Map<Id,QQ__C>([select id,Total__c from QQ__C where id in :QQIdset]);// Now a map with desired QQ records is ready
		//Loop through the opportunities to assign the probability by fetching it from the map based on QQ__C field
		
		
		for(Opportunity p : Trigger.new) {
                
				 p.Probability = QQRecordMap.get(p.QQ__c).Total__c;
        }
}

Note: Just try to change the variable names in the tirrger to meaningful names which will make more sense if we look back in future :)

Cheers.,


Hope it helps.,




If it did resolve your question/req, please mark it as solved, so that it might guide others!

Thanks,
Balaji