Mybatis在插入自增字段時，會對當前對象未賦值的自增字段進行賦值

Mybatis在插入自增字段時，會對當前對象未賦值的自增字段進行賦值，以下即自動完成對id的賦值

OrderItem orderItem = new OrderItem();

            System.out.println("==========");
            System.out.println(orderItem);//此時輸出OrderItem{id=null, pid=null, oid=null, uid=null, number=null, product=null}

            orderItem.setPid(pid);
            orderItem.setUid(user.getId());
            orderItem.setNumber(num);
            System.out.println("==========");
            System.out.println(orderItem);//此時輸出OrderItem{id=null, pid=91, oid=null, uid=1, number=1, product=null}


            orderItemService.add(orderItem);


            System.out.println("==========");
            System.out.println(orderItem);//此時輸出OrderItem{id=6, pid=91, oid=null, uid=1, number=1, product=null}