Mongoid random document

Question

Lets say I have a Collection of users. Is there a way of using mongoid to find n random users in the collection where it does not return the same user twice? For now lets say

Answer 1

If you really want simplicity you could use this instead:

class Mongoid::Criteria

  def random(n = 1)
    indexes = (0..self.count-1).sort_by{rand}.slice(0,n).collect!

    if n == 1
      return self.skip(indexes.first).first
    else
      return indexes.map{ |index| self.skip(index).first }
    end
  end

end

module Mongoid
  module Finders

    def random(n = 1)
      criteria.random(n)
    end

  end
end

You just have to call User.random(5) and you'll get 5 random users. It'll also work with filtering, so if you want only registered users you can do User.where(:registered => true).random(5).

This will take a while for large collections so I recommend using an alternate method where you would take a random division of the count (e.g.: 25 000 to 30 000) and randomize that range.