Dynamically set unique indexes with Tire/Elastic Search

contact.rb

class Contact < ActiveRecord::Base

  # Elastic Search
  include Tire::Model::Search
  include Tire::Model::Callbacks

  # Unique Index
  include Tire::UniqueIndex
  unique_index :account_id

  # Relationships
  belongs_to :account

end

unique_index.rb

module Tire
  module UniqueIndex

    def self.included(base)
      base.extend ClassMethods
    end

    module ClassMethods

      private

      def unique_index(field)

        define_method :set_unique_index do
          self.class.index_name self.send(field)
        end

        define_method :fetch_unique_index do
          set_unique_index unless new_record?
        end

        before_save :set_unique_index
        after_initialize :fetch_unique_index

      end

    end

  end
end