gistfile1.rb

class ShippingCalculators::ShippingCalculator < ActiveRecord::Base

  set_table_name 'shipping_calculators'
  serialize :configuration, OpenStruct
  belongs_to :tax_class
  
  def initialize
    @cost = BigDecimal.new("0")
    @taxes = BigDecimal.new("0")
    @gross_cost = BigDecimal.new("0")
    @package_count = 0
  end

  
  # Define this method on the child classes
  def calculate_for
    
  end
  
  def cost
    return @cost
  end
  
  def taxes
    return @taxes
  end
  
  def package_count
    return @package_count
  end
  
  
end




class ShippingCalculators::WeightBased < ShippingCalculators::ShippingCalculator
  
  def calculate_for(document)
    # foo, bar, stuff goes here
  end
  
  
end



class CreateShippingCalculators < ActiveRecord::Migration
  def change
    create_table :shipping_calculators do |t|
      t.string :name
      t.text :configuration
      t.string :type
      t.integer :tax_class_id
    end
  
  end
end



mysql> desc shipping_calculators;
+---------------+--------------+------+-----+---------+----------------+
| Field         | Type         | Null | Key | Default | Extra          |
+---------------+--------------+------+-----+---------+----------------+
| id            | int(11)      | NO   | PRI | NULL    | auto_increment |
| name          | varchar(255) | YES  |     | NULL    |                |
| configuration | text         | YES  |     | NULL    |                |
| type          | varchar(255) | YES  |     | NULL    |                |
| tax_class_id  | int(11)      | YES  |     | NULL    |                |
+---------------+--------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)