//BEFORE UPDATE
public void onBeforeUpdate(List<Opportunity> triggerOld , List<Opportunity> triggerNew , Map<Id,Opportunity> triggerOldMap , Map<Id,Opportunity> triggerNewMap){

    //Recursivity control. Please add inside this IF any method that should NOT be executed more than once.
        if(mustBeExecuted(triggerNewMap.keySet())){
            manageTimestamps(triggerNew, triggerOldMap);
            setVentureClientId(triggerNew);
            rollUpRFSAssignment(triggerNew, triggerNewMap);
        }

private void rollUpRFSAssignment (List<Opportunity> triggerNew, Map<Id, Opportunity> newMap)
{

    for(Opportunity opp : triggerNew)
    {
        opp.RFS_Assignment__c ='';
    }

    for(Opportunity opp : [SELECT ID FROM Opportunity WHERE id in : newMap.keyset()])
    {
        for(RequestforStartupAssignment__c sij : opp.Request_for_Startup_Assignments__r)
        {
            if(newMap.get(opp.Id).Request_for_Startup__c == '')
                newMap.get(opp.Id).Request_for_Startup__c = sij.Request_for_Startup__r.Name;
            else if ( (newMap.get(opp.Id).Request_for_Startup__c + ', ' + sij.Request_for_Startup__r.Name).length() < 254)
                newMap.get(opp.Id).Request_for_Startup__c = newMap.get(opp.Id).Request_for_Startup__c + ', ' + sij.Request_for_Startup__r.Name;
        }
    }
}