Run a single migration file

Question

Assuming fairly recent version of Rails you can always run:

rake db:migrate:up VERSION=20090408054532

Where version is the timestamp in the filename of the migration.

Edit: At some point over the last 8 years (I'm not sure what version) Rails added checks that prevent this from running if it has already been run. This is indicated by an entry in the schema_migrations table. To re-run it, simply execute rake db:migrate:redo VERSION=20090408054532 instead.

You can just run the code directly out of the ruby file:

rails console
>> require "db/migrate/20090408054532_add_foos.rb"
>> AddFoos.new.up

Note: Very old versions of rails may require AddFoos.up rather than AddFoos.new.up.

An alternative way (without IRB) which relies on the fact that require returns an array of class names:

script/runner 'require("db/migrate/20090408054532_add_foos.rb").first.constantize.up'

Note that if you do this, it won't update the schema_migrations table, but it seems like that's what you want anyway.

Additionally, if it can't find the file you may need to use require("./db/..." or try require_relative depending on your working directory

If you want to run a specific migration, do

$ rake db:migrate:up VERSION=20080906120000

If you want to run migrations multiple times, do

# use the STEP parameter if you need to go more than one version back
$ rake db:migrate:redo STEP=3

If you want to run a single migration multiple times, do

# this is super useful
$ rake db:migrate:redo VERSION=20080906120000

(you can find the version number in the filename of your migration)

---

Edit: You can also simply rename your migration file, Eg:

20151013131830_my_migration.rb -> 20151013131831_my_migration.rb

Then migrate normally, this will treat the migration as a new one (usefull if you want to migrate on a remote environment (such as staging) on which you have less control.

Edit 2: You can also just nuke the migration entry in the database. Eg:

rails_c> q = "delete from schema_migrations where version = '20151013131830'"
rails_c> ActiveRecord::Base.connection.execute(q)

rake db:migrate will then rerun the up method of the nuked migrations.

If you've implemented a change method like this:

class AddPartNumberToProducts < ActiveRecord::Migration
  def change
    add_column :products, :part_number, :string
  end
end

You can create an instance of the migration and run migrate(:up) or migrate(:down) on an instance, like this:

$ rails console
>> require "db/migrate/20090408054532_add_part_number_to_products.rb"
>> AddPartNumberToProducts.new.migrate(:down)

This are the steps to run again this migration file "20150927161307_create_users.rb"

1. Run the console mode. (rails c)

2. Copy and past the class which is in that file to the console.

   class CreateUsers < ActiveRecord::Migration
     def change
       create_table :users do |t|
         t.string :name
         t.string :email
         t.timestamps null: false   end
       end
     end
   end
   

3. Create an instance of the class CreateUsers: c1 = CreateUsers.new

4. Execute the method change of that instance: c1.change

As of rails 5 you can also use rails instead of rake

Rails 3 - 4

# < rails-5.0
rake db:migrate:up VERSION=20160920130051

Rails 5

# >= rails-5.0
rake db:migrate:up VERSION=20160920130051

# or

rails db:migrate:up VERSION=20160920130051