Rails select random record

Question

I don\'t know if I\'m just looking in the wrong places here or what, but does active record have a method for retrieving a random object?

Something like?

<         


        

Answer 1

We found that offsets ran very slowly on MySql for a large table. Instead of using offset like:

model.find(:first, :offset =>rand(c))

...we found the following technique ran more than 10x faster (fixed off by 1):

max_id = Model.maximum("id")
min_id = Model.minimum("id")
id_range = max_id - min_id + 1
random_id = min_id + rand(id_range).to_i
Model.find(:first, :conditions => "id >= #{random_id}", :limit => 1, :order => "id")

Answer 2

If you would need a random record but only within certain criteria you could use "random_where" from this code:

module ActiveRecord
  class Base
    def self.random
      if (c = count) != 0
        find(:first, :offset =>rand(c))
      end
    end

    def self.random_where(*params)
      if (c = where(*params).count) != 0
        where(*params).find(:first, :offset =>rand(c))
      end
    end

  end
end

For e.g :

@user = User.random_where("active = 1")

This function is very useful for displaying random products based on some additional criteria