I needed to save my products in the session for the cart. My product has a belongs_to relationship with a picture object, which has the full data in the DB (20+ Kb/picture).

Obviously, saving the whole products database in the session would be unfeasible. So, I dug into the Ruby Marshal class documentation, and came up with the following solution:

 1 class Product < ActiveRecord::Base
 2   def _dump(ignored)
 3     self.id.to_s
 4   end
 6   def self._load(id)
 7     find(id)
 8   end
 9 end

Instead of saving the whole object, what I’m saving is only the model’s ID. On reload, I simply fetch the object from the DB again. That way, my sessions stay nice and small, but I have the full object at my disposal when I want to work with the object.

One last thing. I coded a test which makes sure that things will always stay nice and small:

 1 class ProductTest < Test::Unit::TestCase
 2   def test_dumping_loading
 3     prod = Product.find(:first)
 4     stream = Marshal.dump(prod)
 5     assert stream.length < 32,
 6         "Dumped stream exceeds 20 bytes treshold: #{stream.size}"
 7     assert_equal prod, Marshal.load(stream)
 8   end
 9 end


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I am François Beausoleil, a Ruby on Rails and Scala developer. During the day, I work on Seevibes, a platform to measure social interactions related to TV shows. At night, I am interested many things. Read my biography.

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