code: public function onInsert(ResourceEventInterface $event)
      {
          $item = $this->getSupplierOrderItemFromEvent($event);
  
          $changed = $this->synchronizeWithProduct($item);
  
          if ($changed) {
              $this->persistenceHelper->persistAndRecompute($item);
  
              $this->scheduleSupplierOrderContentChangeEvent($item->getOrder());
          }
  
          // If supplier order state is 'ordered', 'partial' or 'completed'
          if (SupplierOrderStates::isStockableState($item->getOrder()->getState())) {
              // Associated stock unit (if not exists) must be created (absolute ordered quantity).
              $this->stockUnitLinker->linkItem($item);
          } else { // Supplier order state is 'new' or 'canceled'
              // Associated stock unit (if exists) must be deleted.
              $this->stockUnitLinker->unlinkItem($item);
          }
      }
docs: Insert event handler.
  
  @param ResourceEventInterface $event