Trying to write trigger on Order item .I have created new field called discount.I have to perform formula using trigger on TotalPrice `(TotalPrice = Discount * TotalPrice)`. I am not able to access TotalPrice hence getting this error "Innvalid field TotalPrice for SObject OrderItem
"
Not understanding how to access TotalPrice fields .


    trigger Totalprice on OrderItem (after insert,after update)  {
         if(trigger.isafter && trigger.isupdate){
              for(OrderItem oi : trigger.new) {
                  Oi.TotalPrice =  Oi.Discount__c * Oi.TotalPrice;
              }   
         }   
    }