Each change in the database schema has its own migration object, encapsulating a move up and a move down. Listing 1 shows an empty migration.

数据库模式中的每个变化都有自己的迁移对象，迁移对象包装了前进和后退。

youdao

When using padding, anchor the pillow down with a sand bag or a non-reflecting heavy object so it doesn't move.

当使用填充物的时候，要用沙袋或者不会有声反射的重物把它压着，这样它就不会移动。

youdao