find_random.rb

class ActiveRecord::Relation

  # Returns no more than n records, chosen at random
  #
  # @param [Integer] n
  # @return [ActiveRecord::Base, nil]
  #   When n == 1
  # @return [Array]
  #   When n > 1
  #   
  def find_random( n = 1 )
    raise ArgumentError if n < 1

    sql = select( primary_key ).to_sql

    ids = connection.
      execute( sql ).
      to_a.
      shuffle.
      take( n ).
      map( &:first )

    find( *ids )
  end

end


class ActiveRecord::Base

  def self.find_random( n = 1 )
    scoped.find_random( n )
  end

end