class OrderItemTypeExtension extends AbstractTypeExtension
{

    public static function getExtendedTypes(): iterable
    {
        yield OrderItemType::class;
    }
    

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            //取引区分
            ->add('transact_kbn', TextType::class, [
                'required' => false,
                'data' => '0',
              ])     
            //単位区分（規格管理コード）
            ->add('backend_name', TextType::class, [
                'required' => false,
              ]);                                 

    }

}

/**
 * @CartFlow
 * @ShoppingFlow
 * @OrderFlow
 * OrderItemのカスタマイズ.
 */
class CustomOrderItemProcessor extends AbstractPurchaseProcessor
{
    /**
     * @var EccubeConfig
     */
    private $eccubeConfig;

    /**
     * @var OrderRepository
     */
    private $orderRepository;

    /**
     * OrderNoProcessor constructor.
     *
     * @param EccubeConfig $eccubeConfig
     * @param OrderRepository $orderRepository
     */
    public function __construct(EccubeConfig $eccubeConfig, OrderRepository $orderRepository)
    {
        $this->eccubeConfig = $eccubeConfig;
        $this->orderRepository = $orderRepository;
    }
	
	/**
     * {@inheritdoc}
     */
    public function prepare(ItemHolderInterface $itemHolder, PurchaseContext $context)
    {
        // Order以外の場合は何もしない
        if (!$itemHolder instanceof Order) {
            return;
        }

        foreach ($itemHolder->getProductOrderItems() as $item) {
            $Product = $item->getProduct();
			if( empty($Product) ) continue;
			
			// 追加した項目の再セット
			$item->setTransactKbn($Product->getTransactKbn());
        }

        // Order以外の場合は何もしない
        if (!$itemHolder instanceof Order) {
            return;
        }        	
        foreach ($itemHolder->getProductOrderItems() as $item) {
            $Product = $item->getClassCategoryName1();
			if( empty($ClassCategory) ) continue;
			
			// 追加した項目の再セット
			$item->setBackendName($ClassCategory->getBackendName());
        }
    }

}

<!-- 取引区分 -->
                     <td class="align-middle">
                       <div class="col-12 col-xl-8">
                             {{ OrderItem.transact_kbn }}                                       
                                                </div>
                                            </td>