/**
  * Delete all items for a invoice
  *
  * @param Invoice $invoice
  * @return null
  */
 function deleteByInvoice($invoice)
 {
     db_begin_work();
     $execute = db_execute('DELETE FROM ' . TABLE_PREFIX . 'invoice_time_records WHERE invoice_id = ?', $invoice->getId());
     if ($execute && !is_error($execute)) {
         $delete = InvoiceItems::delete(array('invoice_id = ?', $invoice->getId()));
         if ($delete && !is_error($delete)) {
             db_commit();
         } else {
             db_rollback();
         }
         // if
         return $delete;
     } else {
         db_rollback();
         return $execute;
     }
     // if
 }