fix: V9迁移使用DO块处理外键约束

src/main/resources/db/migration/V9__fix_product_foreign_key.sql

@@ -1,5 +1,4 @@
 -- 修改商品表外键约束，级联删除（库存、库存流水）
--- 但订单明细不级联删除，因为已冗余保存商品信息
 ALTER TABLE stock DROP CONSTRAINT IF EXISTS stock_product_id_fkey;
 ALTER TABLE stock ADD CONSTRAINT stock_product_id_fkey 
     FOREIGN KEY (product_id) REFERENCES products(product_id) ON DELETE CASCADE;
@@ -8,7 +7,13 @@ ALTER TABLE stock_flow DROP CONSTRAINT IF EXISTS stock_flow_product_id_fkey;
 ALTER TABLE stock_flow ADD CONSTRAINT stock_flow_product_id_fkey 
     FOREIGN KEY (product_id) REFERENCES products(product_id) ON DELETE CASCADE;
 
--- 订单明细不再级联删除（已冗余保存商品信息）
-ALTER TABLE order_items DROP CONSTRAINT IF EXISTS order_items_product_id_fkey;
+-- 订单明细不级联删除（已冗余保存商品信息）
+-- 如果约束已存在则修改，不存在则忽略
+DO $$ 
+BEGIN
+    IF EXISTS (SELECT 1 FROM information_schema.table_constraints WHERE constraint_name = 'order_items_product_id_fkey') THEN
+        ALTER TABLE order_items DROP CONSTRAINT IF EXISTS order_items_product_id_fkey;
+    END IF;
+END $$;
 ALTER TABLE order_items ADD CONSTRAINT order_items_product_id_fkey 
     FOREIGN KEY (product_id) REFERENCES products(product_id);