A Single Programmer's Blog

A bit more than a year ago, I wrote about model serialization in session, in which I advocated to implement dump and load methods in your model to only marshal the object’s ID instead of the full object’s properties.

Today, I found about the object_id_session plugin, which has the same purpose, but a different implementation.

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

 5 

 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