Using veritas as a pseudo EV replacement in datamapper

embedded_items.rb

# this is full of bad metaprogramming
class EmbeddedItems < DataMapper::Mongo::Property::Array
  def load(value)
    if value.nil?
      nil
    elsif value.is_a? ::Array
      value.map { |item| embedded_item_class.load item }.extend collection
    else
      raise ArgumentError.new "+value+ of a property of #{self.class} type must be ::Array was: #{value.class}"
    end
  end

  def embedded_item_class
    self.class::EMBEDDED_ITEM
  end

  def collection
    self.class::Collection
  end

  def dump(value)
    if value.nil?
      nil
    elsif value.is_a? ::Array
      value.map do |item| 
        if item.is_a? embedded_item_class
          item.attributes
        else
          raise ArgumentError.new "each item of a property of #{self.class} type must be ::#{embedded_item_class} was: #{value.class}"
        end
      end
    else
      raise ArgumentError.new "+value+ of a property of #{self.class} type must be ::Array was: #{value.class}"
    end
  end

  def typecast(value)
    if value.nil?
      nil
    elsif value.is_a? ::Array
      value.map do |item| 
        if item.kind_of? embedded_item_class
          item
        else
          embedded_item_class.load item 
        end
      end.extend collection
    else
      raise ArgumentError.new "+value+ of a property of #{self.class} type must be ::Array was: #{value.class}"
    end
  end

  class << self
    def for(klass)
      unless klass.is_a? ::Class
        raise ArgumentError.new "+klass+ msut be of type ::Class was: #{value.class}"
      end
      return registry[klass] if registry[klass]
      embedded = Class.new(Stocktrade::Property::EmbeddedItems)
      embedded.const_set('EMBEDDED_ITEM',klass)
      embedded.const_set('Collection',Module.new)
      registry[klass]=embedded
    end

    def registry
      @registry ||= {}
    end
  end
end

line_item.rb

require 'virtus'

class LineItem
  include Virtus
  include Virtus::DirtyTracking
  include ActiveModel::Validations

  attribute :product_id, String
  attribute :quantity, Integer

  validates_presence_of :product_id
  validates_presence_of :quantity

  def product=(value)
    @product_id = if value.nil?
      nil
    elsif value.is_a? Product
      raise ArgumentError, 'product must have an id' unless value.id
      value.id
    else
      raise ArgumentError, '+value+ must be nil or an instance of Product'
    end
  end

  def product
    Product.get(product_id) if product_id
  end


  def self.load(value)
    if value.kind_of? ::Hash
      self.new(value)
    else
      raise ArgumentError, "+value+ must be an Hash was: #{value.class}"
    end
  end

  def ==(other)
    return false unless other.kind_of?(self.class)
    other.product_id == self.product_id && other.quantity == self.quantity
  end
end

order.rb

class Order
  include DataMapper::Mongo::Resource
  property :id,ObjectId
  property :line_items,      ::EmbeddedItems.for(LineItem)
end