备份：PWA配置前的完整版本

包含所有最新开发的功能和修复，作为PWA正确配置前的备份点。

backend/routes/purchase-orders.js

@@ -203,7 +203,7 @@ router.put('/:id', async (req, res) => {
       WHERE id = ?
     `, [supplier_id, supplier_country, contract_url, quotation_url, remark, id]);
     
-    if (result.changes === 0) {
+    if (result.rowCount === 0) {
       return res.status(404).json({ success: false, message: '采购订单不存在' });
     }
     
@@ -303,7 +303,7 @@ router.post('/:id/cancel', async (req, res) => {
       [id]
     );
     
-    if (result.changes === 0) {
+    if (result.rowCount === 0) {
       return res.status(404).json({ success: false, message: '采购订单不存在' });
     }
     
@@ -391,7 +391,7 @@ router.put('/:id/items/:itemId', async (req, res) => {
       WHERE id = ? AND purchase_order_id = ?
     `, [product_id, product_name, specification, unit, quantity, unit_price, total_price, itemId, id]);
     
-    if (result.changes === 0) {
+    if (result.rowCount === 0) {
       return res.status(404).json({ success: false, message: '商品明细不存在' });
     }
     
@@ -418,7 +418,7 @@ router.delete('/:id/items/:itemId', async (req, res) => {
       [itemId, id]
     );
     
-    if (result.changes === 0) {
+    if (result.rowCount === 0) {
       return res.status(404).json({ success: false, message: '商品明细不存在' });
     }
     
@@ -506,7 +506,7 @@ router.put('/:id/payment-plans/:planId', async (req, res) => {
       WHERE id = ? AND purchase_order_id = ?
     `, [stage, planned_date, planned_amount, planned_percentage, remark, planId, id]);
     
-    if (result.changes === 0) {
+    if (result.rowCount === 0) {
       return res.status(404).json({ success: false, message: '付款计划不存在' });
     }
     
@@ -533,7 +533,7 @@ router.delete('/:id/payment-plans/:planId', async (req, res) => {
       [planId, id]
     );
     
-    if (result.changes === 0) {
+    if (result.rowCount === 0) {
       return res.status(404).json({ success: false, message: '付款计划不存在' });
     }