Rails: How to add add_index to existing table

Question

I already migrated a table called units with several columns. I was wondering how to migrate in a stand alone \'add_index\' to this table using the cmd. Is this code correct:

Answer 1

Almost

class AddIndexToUnits < ActiveRecord::Migration
  def self.up
    add_index :units, :lesson_id, :name=>'lesson_index'
  end

  def self.down
    remove_index :units, 'lesson_index'
  end
end