fallback handled

app/Http/Controllers/Admin/ProductController.php

@@ -460,6 +460,12 @@ class ProductController extends SuperController
             $data['use_last_price_if_zero'] = !empty($data['use_last_price_if_zero']);
         }
 
+        if (!Product::hasTradeByQuantityColumn()) {
+            unset($data['trade_by_quantity']);
+        } elseif (array_key_exists('trade_by_quantity', $data)) {
+            $data['trade_by_quantity'] = !empty($data['trade_by_quantity']);
+        }
+
         if (!Product::hasDirectPriceColumn()) {
             unset($data['direct_price']);
         }

app/Http/Controllers/Controller.php

@@ -451,6 +451,16 @@ class Controller extends BaseController
         return (float) $product['amount'] > 0;
     }
 
+    /** معامله مقداری: فقط فیلد trade_by_quantity */
+    public static function usesQuantityTrade($product): bool
+    {
+        $value = is_array($product)
+            ? ($product['trade_by_quantity'] ?? null)
+            : (is_object($product) ? ($product->trade_by_quantity ?? null) : null);
+
+        return !empty($value);
+    }
+
     /** ضریب قیمت محصول — بدون وزن قطعه همیشه ۱ */
     public static function productPriceMultiplier($product): float
     {