这也许是真的，但它只是部分情况。
只是部分情况下不需要迁移，一旦你需要将你的程序投入生产应用中去，那么迁移是仍然需要的，因为你已经告诉DB如何修改以保存信息。
This is partly true. Migrations are still required once you have your app in production, because you have to tell the DB how to change itself in a way that preserves information.
对于大部分情况来说，对象没有自己的生命——它们只是在运行线程调用它们的方法时才存在。
Objects, for the most part, don't have a life of their own — they only briefly come alive as running threads invoke methods on them.
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