How to rollback just one step using rake db:migrat

问题:

After adding migration files in the db/migrate folder and running rake db:migrate, I want get back to the previous step, I think using VERSION=n is 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?

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

回答1:

For starters

rake db:rollback will get you back one step

then

rake db:rollback STEP=n

Will roll you back n migrations where n is the number of recent migrations you want to rollback.

More references here.

回答2:

Roll back the most recent migration:

rake db:rollback

Roll back the n most recent migrations:

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.

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Here's some more:

• 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 n migrations and run them again
• rake db:migrate:up VERSION=20080906120000 - Run the up method for the given migration
• rake db:migrate:down VERSION=20080906120000 - Run the down method for the given migration

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

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

$ rake db:migrate VERSION=20080906120000

(From Running Migrations in the Rails Guides)

回答3:

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

rails db:migrate:up VERSION=timestamp

Now how you get the timestamp. Go to this path

/db/migrate

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

回答4:

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

• rake db:migrate:status gives 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

回答5:

If the version is 20150616132425, then use:

rails db:migrate:down VERSION=20150616132425