Add TokenAuthenticatable to an existing user model for devise

datestamp_add_token_authenticatable_to_users.rb

# remember to add "devise :token_authenticatable" to user.rb
# and uncomment "config.token_authentication_key = :auth_token" from devise.rb
class AddTokenAuthenticatableToUsers < ActiveRecord::Migration
  def self.up
    change_table(:users) do |t|
      t.token_authenticatable
    end
    User.reset_column_information

    User.all.each do |user|
      user.ensure_authentication_token
      user.save
    end
  end

  def self.down
    remove_column :users, :authentication_token
  end
end