假设您想重用上面的例子，并加上一个更新产品库存，即减去购物订单中每项产品的产品数量的操作。
Suppose you want to reuse the example above and add another operation that updates the product inventory, decreasing the product quantity for each item in the purchase order.
这些迁移操作都会保存，并加上时间戳，让我们可以回滚到数据库结构的上一个版本。
These migrations are all saved and time-stamped, to make it possible to roll back to previous versions of the data structure.
由此应用程序创建的用户界面从为电话屏幕定义一个显示并附加上一个Form开始。
The user interface initiative by this application begins by defining a display for the phone screen and attaching a Form to it.
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