Ruby on Rails. Module to handle 'quantity' attributes by overriding the << and delete methods of the has_many association

gistfile1.rb

class Package < ActiveRecord::Base
  has_many :products, :through => :packagings, extend => QuantityAssociation

  # ... do stuff

end

module QuantityAssociation

  def include_duplicates
    return_array = []
    through_collection.each do |through|
      associate = through.send(reflection_name)
      return_array.concat Array.new(through.quantity || 1).fill( associate )
    end
    return_array
  end

  def <<(*records)
    result = true
    load_target if proxy_association.owner.new_record?

    transaction do
      flatten_deeper(records).each do |record|
        existing = get_existing_through record
        if existing.present?
          existing.increment! :quantity
        else
          result &&= super(record)
        end
      end
    end

    result && self
  end

  def delete(*records)
    transaction do
      flatten_deeper(records).each do |record|
        existing = get_existing_through record
        if existing.present? and existing.quantity.present? and existing.quantity > 1
          existing.decrement! :quantity
        else
          super(record)
        end
      end
    end
  end

private

  def reflection_name
    proxy_association.source_reflection.name
  end

  def through_source_key
    proxy_association.reflection.source_reflection.foreign_key
  end

  def through_name
    proxy_association.reflection.through_reflection.name
  end

  def through_collection
    proxy_association.owner.send through_name
  end

  def get_existing_through record
    through_collection.where("#{through_source_key}" => record.id).try(:first)
  end

  def flatten_deeper(array)
    array.collect { |element| (element.respond_to?(:flatten) && !element.is_a?(Hash)) ? element.flatten : element }.flatten
  end

end

#--------
#--------

# Means you can just do things like

package = Package.first
package.products << Product.first

# and if the product is already associated, the 'quantity' column will be 
# incremented on the 'packagings' table

The 'get_existing_through' method could well be done simpler. Anyone know a better way?