Add index on composite keys using Rails migration

add_index_to_composite_keys.rb

  def change
    create_table :users do |t|
      t.references :account #account_id
      t.references :profile #profile_id
      #...
    end

    add_index :accounts, [:account_id, :token], :unique => true, :name => 'by_account_token'
    add_index :accounts, :profile_id, :unique => true, :name => 'by_profile'
    add_index :accounts, [:account_id, :display_name],  :name => 'by_account_profile'
    #...
  end