需要了解我是否应该使用PHP的Session变量

I am writing a PHP plugin for a WooCommerce site. It is just a single PHP file.

It contains two main functions that execute via PHP's add_action on two different web pages. I am having difficulty passing shopping cart item codes to the order processed page. I think I need to use SESSION state variables. Just wondering whether for each website page you need to have a separate PHP file? Or just create a SESSION state variable to hold the partNumber.

Thanks

So this is what I have already tried:-

1. SESSION State to hold $partNumber. Couldn't get it to work - Data not retained.

2. I declared $partNumber outside any functions and then tried to reference it using the global keyword within functions but when the second function (ts_email_after_order_table) is invoked using an add_action the data inside $partNumber is lost.

   $partNumber;
   
   function getCartItems()
   {
       global $woocommerce;
       global $partNumber;
   
       $items = $woocommerce->cart->get_cart();
   
       foreach($items as $item => $values) {
          $product =  wc_get_product( $values['data']->get_id() );
          $getProductDetail = wc_get_product( $values['product_id'] );
          $partNumber = $product ->get_sku(); 
          echo $partNumber;
       }
   }
   
   function ts_email_after_order_table( $order, $sent_to_admin, 
                        $plain_text, $email )
   { 
       global $partNumber // Data is lost here
       echo $order;
       '''''
   }
   

I need to see that the $partNumber retains it's value inside the ts_email_after_order_table function. It's null.