[ruby-on-rails] How to rollback a specific migration?

I have the following migration file db\migrate\20100905201547_create_blocks.rb

How can I specifically rollback that migration file?

Migrations change the state of the database using the command

$ bundle exec rake db:migrate

We can undo a single migration step using

  $ bundle exec rake db:rollback

To go all the way back to the beginning, we can use

  $ bundle exec rake db:migrate VERSION=0

As you might guess, substituting any other number for 0 migrates to that version number, where the version numbers come from listing the migrations sequentially

Well in rails 5 it's quite easy rake db:migrate:status or rails db:migrate:status

It was modified to handle both the same way Then just pick which Version you want to roll back and then run rake db:migrate VERSION=2013424230423

Make sure VERSION is all capital letters

If you have a problem with any step of the migration or stuck in the middle simply go to the migration file and comment out the lines that were already migrated.

Hope that helps

Rolling back last migration:

# rails < 5.0
rake db:rollback

# rails >= 5.0
rake db:rollback
# or
rails db:rollback

Rolling back last n number of migrations

# rails < 5.0
rake db:rollback STEP=2

# rails >= 5.0
rake db:rollback STEP=2
# or
rails db:rollback STEP=2

Rolling back a specific migration

# rails < 5.0
rake db:migrate:down VERSION=20100905201547

# rails >= 5.0
rake db:migrate:down VERSION=20100905201547
# or
rails db:migrate:down VERSION=20100905201547

You can rollback your migration by using rake db:rollback with different options. The syntax will be different according to your requirements.

If you want to rollback just the last migration, then you can use either

rake db:rollback

or

rake db:rollback STEP=1

If you want rollback number of migrations at once, then you simply pass an argument:

rake db:rollback STEP=n

where n is number of migrations to rollback, counting from latest migration.

If you want to rollback to a specific migration, then you should pass the version of the migration in the following:

rake db:migrate:down VERSION=xxxxx

where xxxxx is the version number of the migration.

In Addition

When migration you deployed long ago does not let you migrate new one.

What happened is, I work in a larger Rails app with more than a thousand of migration files. And, it takes a month for us to ship a medium-sized feature. I was working on a feature and I had deployed a migration a month ago then in the review process the structure of migration and filename changed, now I try to deploy my new code, the build failed saying

ActiveRecord::StatementInvalid: PG::DuplicateColumn: ERROR:  column "my_new_field" of relation "accounts" already exists

none of the above-mentioned solutions worked for me because the old migration file was missing and the field I intended to create in my new migration file already existed in the DB. The only solution that worked for me is:

1. I scped the file to the server
2. I opened the rails console
3. I required the file in the IRB session
4. then AddNewMyNewFieldToAccounts.new.down

then I could run the deploy build again.

Hope it helps you too.

If you want to rollback and migrate you can run:

rake db:migrate:redo

That's the same as:

rake db:rollback
rake db:migrate

To rollback the last migration you can do:

rake db:rollback

If you want to rollback a specific migration with a version you should do:

rake db:migrate:down VERSION=YOUR_MIGRATION_VERSION

If the migration file you want to rollback was called db/migrate/20141201122027_create_some_table.rb, then the VERSION for that migration is 20141201122027, which is the timestamp of when that migration was created, and the command to roll back that migration would be:

rake db:migrate:down VERSION=20141201122027

To roll back all migrations up to a particular version (e.g. 20181002222222), use:

rake db:migrate VERSION=20181002222222

(Note that this uses db:migrate -- not db:migrate:down as in other answers to this question.)

Assuming the specified migration version is older than the current version, this will roll back all migrations up to, but not including, the specified version.

For example, if rake db:migrate:status initially displays:

  (... some older migrations ...)
  up      20181001002039  Some migration description
  up      20181002222222  Some migration description
  up      20181003171932  Some migration description
  up      20181004211151  Some migration description
  up      20181005151403  Some migration description

Running:

rake db:migrate VERSION=20181002222222

Will result in:

  (... some older migrations ...)
  up      20181001002039  Some migration description
  up      20181002222222  Some migration description
  down    20181003171932  Some migration description
  down    20181004211151  Some migration description
  down    20181005151403  Some migration description

Reference: https://makandracards.com/makandra/845-migrate-or-revert-only-some-migrations

rake db:migrate:down VERSION=20100905201547

will roll back the specific file.

To find the version of all migrations, you can use this command:

rake db:migrate:status

Or, simply the prefix of the migration's file name is the version you need to rollback.

See the Ruby on Rails guide entry on migrations.

rake db:migrate:down VERSION=your_migrations's_version_number_here

The version is the numerical prefix on the migration's file name

How to find version:

Your migration files are stored in your rails_root/db/migrate directory. Find appropriate file up to which you want to rollback and copy the prefix number.

for example

file name: 20140208031131_create_roles.rb then the version is 20140208031131

If it is a reversible migration and the last one which has been executed, then run rake db:rollback. And you can always use version. e.g

the migration file is 20140716084539_create_customer_stats.rb,so the rollback command will be, rake db:migrate:down VERSION=20140716084539

From Rails Guide

Reverting Previous Migrations

You can use Active Record's ability to rollback migrations using the revert method:

require_relative '20100905201547_create_blocks'

class FixupCreateBlock < ActiveRecord::Migration
  def change
    revert CreateBlock

    create_table(:apples) do |t|
      t.string :variety
    end
  end
end

The revert method also accepts a block of instructions to reverse. This could be useful to revert selected parts of previous migrations. For example, let's imagine that CreateBlock is committed and it is later decided it would be best to use Active Record validations, in place of the CHECK constraint, to verify the zipcode.

    class DontUseConstraintForZipcodeValidationMigration < ActiveRecord::Migration
      def change
        revert do
          # copy-pasted code from CreateBlock
          reversible do |dir|
            dir.up do
              # add a CHECK constraint
              execute <<-SQL
                ALTER TABLE distributors
                  ADD CONSTRAINT zipchk
                    CHECK (char_length(zipcode) = 5);
              SQL
            end
            dir.down do
              execute <<-SQL
                ALTER TABLE distributors
                  DROP CONSTRAINT zipchk
              SQL
            end
          end

          # The rest of the migration was ok
        end
      end
    end

The same migration could also have been written without using revert but this would have involved a few more steps: reversing the order of create_table and reversible, replacing create_table by drop_table, and finally replacing up by down and vice-versa. This is all taken care of by revert.

To rollback the last migration you can do:

rake db:rollback

If you want to rollback a specific migration with a version you should do:

rake db:migrate:down VERSION=YOUR_MIGRATION_VERSION

For e.g. if the version is 20141201122027, you will do:

rake db:migrate:down VERSION=20141201122027

to rollback that specific migration.