aiaio

module SelectiveAttributeValidatable

  def self.included(base)
    base.send(:include, InstanceMethods)

    base.class_eval do
      alias_method_chain :update_attributes, :check
    end
  end

aiaio

validates_presence_of   :first_name, :if => :should_require_first_name?
validates_uniqueness_of :url_slug,   :if => :should_require_url_slug?

aiaio

class Product < ActiveRecord::Base

  has_many :images, :class_name => "ProductImage"

end

class ProductImage < ActiveRecord::Base

  belongs_to :product

aiaio

ProductImagesDefinitions = {
  'main'   => {:styles => {:large => "1200x600!", :medium => "600x300!"},

  'header' => {:styles => {:large => "400x600!", :medium => "200x300!"}
}

aiaio

# Create product images.
@product.product_images.create(:label => 'main',   :image => # Attachment object)
@product.product_images.create(:label => 'header', :image => # Attachment object)

# Access product images.
@product.available_images('main')
@product.available_images('header')

aiaio

# Adds behavior for getting, setting, and validating 
# images for any given model. Relies on RAILS_ROOT/config/image_definitions.rb
module ImageHandling

  def self.included(base)

    base.class_eval do 
      # Defines accessor names: if the class is Book, 
      # names will be #book_images and #book_images=
      image_accessor_name = self.to_s.underscore + "_images"