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    <p>You can put that code into your 'lib' directory saving as find_random.rb</p> <pre><code>module FindRandom # pull out a unique set of random active record objects without killing # the db by using "order by rand()" # Note: not true-random, but good enough for rough-and-ready use # # The first param specifies how many you want. # You can pass in find-options in the second param # examples: # Product.random =&gt; one random product # Product.random(3) =&gt; three random products in random order # # Note - this method works fine with scopes too! eg: # Product.in_stock.random =&gt; one random product that fits the "in_stock" scope # Product.in_stock.random(3) =&gt; three random products that fit the "in_stock" scope # Product.best_seller.in_stock.random =&gt; one random product that fits both scopes # def find_random(num = 1, opts = {}) # skip out if we don't have any return nil if (max = self.count(opts)) == 0 # don't request more than we have num = [max,num].min # build up a set of random offsets to go find find_ids = [] # this is here for scoping # get rid of the trivial cases if 1 == num # we only want one - pick one at random find_ids = [rand(max)] else # just randomise the set of possible ids find_ids = (0..max-1).to_a.sort_by { rand } # then grab out the number that we need find_ids = find_ids.slice(0..num-1) if num != max end # we've got a random set of ids - now go pull out the records find_ids.map {|the_id| first(opts.merge(:offset =&gt; the_id)) } end end </code></pre> <p>and extend your model like that </p> <pre><code>class Car &lt; ActiveRecord::Base extend FindRandom def self.tag_nr self.random end end </code></pre> <p>Calling Car.tag_nr will give you an instance, but something is wrong with your code if you trying to create new instance using other same class instance.</p>
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    1. USIvan Shamatov
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