diff --git a/src/models/OrderProduct.php b/src/models/OrderProduct.php
index 5c4d7be..efb4ce4 100644
--- a/src/models/OrderProduct.php
+++ b/src/models/OrderProduct.php
@@ -87,35 +87,33 @@ public function validate(): array
         return $errors;
     }
 
-    public static function getByID(int $order_id, int $product_id = null): ?OrderProduct
+    /**
+     * order_id and product_id are the primary of the record to be searched.
+     * @param int $order_id
+     * @param int $product_id
+     * @return OrderProduct|null
+     */
+    public static function getByID(int $order_id, int $product_id): ?OrderProduct
     {
-    $query = 'SELECT * FROM order_product WHERE order_id = :order_id';
-    $params = ['order_id' => $order_id];
-
-    if ($product_id !== null) {
-        $query .= ' AND product_id = :product_id';
-        $params['product_id'] = $product_id;
-    }
+        $query = 'SELECT * FROM order_product WHERE order_id = ? and product_id= ?';
+        $params = [$order_id, $product_id];
 
-    $result = self::query($query, $params);
-    if (empty($result)) {
-        return null;
-    }
+        $result = self::query($query, $params);
+        if (empty($result)) {
+            return null;
+        }
 
-    // Assuming there's only one product for a given order if product_id is not provided
-    if ($product_id === null) {
         $result = $result[0];
-    }
 
-    return new OrderProduct(
-        product_id: $result->product_id,
-        cup_size: $result->cup_size,
-        milk_type: $result->milk_type,
-        quantity: $result->quantity,
-        unit_price: (float)$result->unit_price,
-        order_id: $result->order_id,
-    );
-   }
+        return new OrderProduct(
+            product_id: $result->product_id,
+            cup_size: $result->cup_size,
+            milk_type: $result->milk_type,
+            quantity: $result->quantity,
+            unit_price: (float)$result->unit_price,
+            order_id: $result->order_id,
+        );
+    }
 
     public function getOrderID(): int
     {