daily random shuffle

migration.rb

class WidgetShuffleMigration
  def change
    change_table :widgets do |t|
      # used to store the result of a rand() function, which satisifies: 0 < rand() < 1
      t.float :shuffle_order, index: true
    end
  end
end

widget.rb

class Widget < ActiveRecord::Base

  # Reorder is an AR thing that will clear any previous order clauses,
  # which is important when you're trying to shuffle things.
  scope :shuffled, -> { reorder("shuffle_order") }

  # Seed value must be numeric; defaults to yearmonthday
  # Which means that the shuffle will produce the same results during the same day
  def self.shuffle(seed = :default)
    if seed == :default
      seed = Date.today.strftime("%Y%m%d")
    end

    seed = connection.quote(seed)
    update_all "shuffle_order = rand(#{seed})"
  end
   
end