Move item to another order

server/db/database.js

@@ -594,7 +594,7 @@ export default class DBAdapter {
             }
             
             const item = await connection.query(
-                'SELECT id, order_id FROM order_items WHERE id = ? FOR UPDATE', 
+                'SELECT id, order_id, product_id, quantity FROM order_items WHERE id = ? FOR UPDATE', 
                 [itemId]
             );
 
@@ -608,11 +608,35 @@ export default class DBAdapter {
                 });
             }
 
-            await connection.query(
+            if (itemRow.order_id === targetOrderId) {
-                'UPDATE order_items SET order_id = ? WHERE id = ?',
+                await connection.rollback();
-                [targetOrderId, itemId]
+                connection.release();
+                return;
+            }
+
+            const targetItem = await connection.query(
+                'SELECT id, quantity FROM order_items WHERE order_id = ? AND product_id = ? FOR UPDATE',
+                [targetOrderId, itemRow.product_id]
             );
 
+            const targetItemRow = targetItem?.[0];
+
+            if (targetItemRow) {
+                await connection.query(
+                    'UPDATE order_items SET quantity = ? WHERE id = ?',
+                    [targetItemRow.quantity + itemRow.quantity, targetItemRow.id]
+                );
+                await connection.query(
+                    'DELETE FROM order_items WHERE id = ?',
+                    [itemId]
+                );
+            } else {
+                await connection.query(
+                    'UPDATE order_items SET order_id = ? WHERE id = ?',
+                    [targetOrderId, itemId]
+                );
+            }
+
             await connection.commit();
             connection.release();