Ruby-on-rails 如何使用 rake db:migrate 仅回滚一步

How to rollback just one step using rake db:migrate

提问by mko

After adding migration files in the db/migratefolder and running rake db:migrate, I want get back to the previous step, I think using VERSION=nis the right way to do that, but I don't know the correct value of n to use. Is there any command to check the current n value?

在文件db/migrate夹中添加迁移文件并运行后rake db:migrate，我想回到上一步，我认为使用VERSION=n是正确的方法，但我不知道要使用的正确值 n。是否有任何命令可以检查当前的 n 值？

It would be great if anyone could provide full instructions on how to use rake db:migrate.

如果有人能提供有关如何使用rake db:migrate.

回答by rwilliams

For starters

对于初学者

rake db:rollbackwill get you back one step

rake db:rollback会让你退一步

then

然后

rake db:rollback STEP=n

rake db:rollback STEP=n

Will roll you back nmigrations where nis the number of recent migrations you want to rollback.

将推出你回来n迁移哪里n是要回滚最近的迁移数。

More references here.

更多参考在这里。

回答by Ajedi32

Roll back the most recent migration:

回滚最近的迁移：

rake db:rollback

Roll back the nmost recent migrations:

回滚n最近的迁移：

rake db:rollback STEP=n

You can find full instructions on the use of Rails migration tasks for rake on the Rails Guide for running migrations.

您可以在Rails Guide for running migrations上找到有关使用 Rails 迁移任务进行 rake 的完整说明。

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Here's some more:

这里还有一些：

• rake db:migrate- Run all migrations that haven't been run already
• rake db:migrate VERSION=20080906120000- Run all necessary migrations (up or down) to get to the given version
• rake db:migrate RAILS_ENV=test- Run migrations in the given environment
• rake db:migrate:redo- Roll back one migration and run it again
• rake db:migrate:redo STEP=n- Roll back the last nmigrations and run them again
• rake db:migrate:up VERSION=20080906120000- Run the upmethod for the given migration
• rake db:migrate:down VERSION=20080906120000- Run the downmethod for the given migration

• rake db:migrate- 运行所有尚未运行的迁移
• rake db:migrate VERSION=20080906120000- 运行所有必要的迁移（向上或向下）以获取给定版本
• rake db:migrate RAILS_ENV=test- 在给定环境中运行迁移
• rake db:migrate:redo- 回滚一次迁移并再次运行
• rake db:migrate:redo STEP=n- 回滚上次n迁移并再次运行它们
• rake db:migrate:up VERSION=20080906120000- 运行up给定迁移的方法
• rake db:migrate:down VERSION=20080906120000- 运行down给定迁移的方法

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And to answer your question about where you get a migration's version number from:

并回答有关从何处获取迁移版本号的问题：

The version is the numerical prefix on the migration's filename. For example, to migrate to version 20080906120000 run

$ rake db:migrate VERSION=20080906120000

版本是迁移文件名的数字前缀。例如，要迁移到版本 20080906120000 运行

$ rake db:migrate VERSION=20080906120000

(From Running Migrationsin the Rails Guides)

（来自Rails 指南中的运行迁移）

回答by Hemali

Best way is running Particular migration again by using down or up(in rails 4. It's change)

最好的方法是通过使用 down 或 up 再次运行特定迁移（在 rails 4. 它的变化）

rails db:migrate:up VERSION=timestamp

rails db:migrate:up 版本=时间戳

Now how you get the timestamp. Go to this path

现在你如何获得时间戳。走这条路

/db/migrate

/db/迁移

Identify migration file you want to revert.pick the timestamp from that file name.

确定要还原的迁移文件。从该文件名中选择时间戳。

回答by ?oàn Ngh?a

If the version is 20150616132425, then use:

如果版本是20150616132425，则使用：

rails db:migrate:down VERSION=20150616132425

回答by BjarneD

Other people have already answered you how to rollback, but you also asked how you could identify the version number of a migration.

其他人已经回答了您如何回滚，但您还询问了如何识别迁移的版本号。

• rake db:migrate:statusgives a list of your migrations version, name and status (up or down)
• Your can also find the migration file, which contain a timestamp in the filename, that is the version number. Migrations are located in folder: /db/migrate

• rake db:migrate:status给出您的迁移版本、名称和状态（向上或向下）的列表
• 您还可以找到迁移文件，其中包含文件名中的时间戳，即版本号。迁移位于文件夹中：/db/migrate