How to create uniq ID ?

metadata.rb

class ProductMetaData

  include Virtus.model
  include ActiveModel::Validations
  include OverrideAttributes

  attribute :id, String
  attribute :product_url, String
  attribute :bread_crumbs, Array[String]
  attribute :retailer_name, String
  attribute :referer_url, String
  attribute :referer_url_text, String
  attribute :html_storage_uri, String
  attribute :created, Integer
  attribute :modified, Integer

  validates :product_url, :presence => true

  def initialize(params)
    time = Time.now.utc.to_i
    @created = time
    @modified = time
    super(params)
    @id = "#{@retailer_name}:#{@modified}"
  end

end

server output

"inspecting {:referer_uri=>\"http://www.pixiemarket.com/white-net-pocket-dress.html\", :referer_uri_text=>\"White Net Pocket Dress\", :product_url=>\"http://www.pixiemarket.com/white-net-pocket-dress.html\", :bread_crumbs=>[\"Home\", \"Dresses\", \"White Net Pocket Dress\"], :retailer_name=>\"PixieMarket\"} before sotring"
"From model attributes are coming as {:id=>\"PixieMarket:1419250486\", :product_url=>\"http://www.pixiemarket.com/white-net-pocket-dress.html\", :bread_crumbs=>[\"Home\", \"Dresses\", \"White Net Pocket Dress\"], :retailer_name=>\"PixieMarket\", :created=>1419250486, :modified=>1419250486}"
"inspecting {:referer_uri=>\"http://www.pixiemarket.com/varsity-sweatshirt-dress.html\", :referer_uri_text=>\"Varsity Sweatshirt Dress\", :product_url=>\"http://www.pixiemarket.com/varsity-sweatshirt-dress.html\", :bread_crumbs=>[\"Home\", \"Dresses\", \"Varsity Sweatshirt Dress\"], :retailer_name=>\"PixieMarket\"} before sotring"
"From model attributes are coming as {:id=>\"PixieMarket:1419250486\", :product_url=>\"http://www.pixiemarket.com/varsity-sweatshirt-dress.html\", :bread_crumbs=>[\"Home\", \"Dresses\", \"Varsity Sweatshirt Dress\"], :retailer_name=>\"PixieMarket\", :created=>1419250486, :modified=>1419250486}"
"inspecting {:referer_uri=>\"http://www.pixiemarket.com/black-sequin-long-top.html\", :referer_uri_text=>\"Black Sequin Long Top\", :product_url=>\"http://www.pixiemarket.com/black-sequin-long-top.html\", :bread_crumbs=>[\"Home\", \"Tops\", \"Black Sequin Long Top\"], :retailer_name=>\"PixieMarket\"} before sotring"
"From model attributes are coming as {:id=>\"PixieMarket:1419250486\", :product_url=>\"http://www.pixiemarket.com/black-sequin-long-top.html\", :bread_crumbs=>[\"Home\", \"Tops\", \"Black Sequin Long Top\"], :retailer_name=>\"PixieMarket\", :created=>1419250486, :modified=>1419250486}"
"inspecting {:referer_uri=>\"http://www.pixiemarket.com/rainbow-knit-top.html\", :referer_uri_text=>\"Rainbow Knit Top\", :product_url=>\"http://www.pixiemarket.com/rainbow-knit-top.html\", :bread_crumbs=>[\"Home\", \"Tops\", \"Rainbow Knit Top\"], :retailer_name=>\"PixieMarket\"} before sotring"
"From model attributes are coming as {:id=>\"PixieMarket:1419250486\", :product_url=>\"http://www.pixiemarket.com/rainbow-knit-top.html\", :bread_crumbs=>[\"Home\", \"Tops\", \"Rainbow Knit Top\"], :retailer_name=>\"PixieMarket\", :created=>1419250486, :modified=>1419250486}"