Salesforce Update Product Schedule from Opportunity Product using Apex Trigger

Update the Product ScheduleDate when the Opportunity Product ServiceDate changes. First we create an OpportunityProduct Trigger to see when ServiceDate changes and parse the amount of days difference between the old and new date.

trigger ProductDateUpdate on OpportunityLineItem (after update) {
   
    for (OpportunityLineItem oli: Trigger.new) {
        OpportunityLineItem oldCloseDate = Trigger.oldMap.get(oli.ID);
        if (oli.ServiceDate != oldCloseDate.ServiceDate) {
            Integer dateval = oldCloseDate.ServiceDate.daysBetween(oli.ServiceDate);
            ProductScheduleUpdate.ScheduleProductUpdate(oli.id, dateval);  
        }
    }
}

The Trigger class then updates all the Product Schedule Dates by the amount of days.

public class ProductScheduleUpdate
{
    public static void ScheduleProductUpdate(String oid, Integer dateval)
    {
           List datelist;
           datelist = [SELECT ScheduleDate FROM OpportunityLineItemSchedule WHERE OpportunityLineItemId =:oid];
           for (Integer k = 0; k < datelist.size(); k++)
               {
               System.debug('DateList = ' + datelist[k]);
               Date mydate=Date.newInstance(datelist[k].ScheduleDate.Year(),datelist[k].ScheduleDate.Month(),datelist[k].ScheduleDate.Day());
               mydate=mydate.addDays(dateval);
               datelist[k].ScheduleDate = mydate;
               update datelist;
               //date datediff = date.parse(datelist[k]);
               }
        
    }
}