gistfile1.rb

class AddIndexes < ActiveRecord::Migration
  def self.up

     change_table(:songs) do |t|
       t.index(:hash_id, :unique => true)
     end

     change_table(:record_songs) do |t|
        t.index([:song_id, :record_id])
     end

  end

  def self.down
     change_table(:songs) do |t|
       t.remove_index :column => :hash_id
     end

     change_table(:record_songs) do |t|
       t.remove_index :column => [:song_id, :record_id]
     end

  end
end