Example of using a custom coder to read and write an array based attribute

array_coder.rb

class ArrayCoder
  def initialize(default = [])
    @default = default
  end

  def dump(object)
    Array(object).join(',')
  end

  def load(string)
    string.present? ? string.split(',') : @default.clone
  end
end

order.rb

class Order < ActiveRecord::Base
  serialize :items, ArrayCoder.new
end