# Now the incoming/outgoing methods are on item, so you can do:
#
#   Item.incoming(:all, :order => 'created_at desc', :limit => 15)
#
# or
#   
#   @asset.items.incoming(:all, :order => 'created_at desc', :limit => 15)
class Item < ActiveRecord::Base
  belongs_to :asset
  def self.incoming(*args)
    with_scope(:find => { :conditions => 'base_amount > 0'}) { find(*args) }
  end

  def self.outgoing(*args)
    with_scope(:find => { :conditions => 'base_amount < 0'}) { find(*args) }
  end
end

class Asset < ActiveRecord::Base
  has_many :items, :dependent => :destroy_all
end

# Now the incoming/outgoing methods are on Item, so you can do:
#
#   Item.incoming(:all, :order => 'created_at desc', :limit => 15)
#
# but, there is also memoization in the Asset
#   
#   @asset.incoming_items(:all, :order => 'created_at desc', :limit => 15)

class Item < ActiveRecord::Base
  belongs_to :asset
  def self.incoming(*args)
    with_scope(:find => { :conditions => 'base_amount > 0'}) { find(*args) }
  end

  def self.outgoing(*args)
    with_scope(:find => { :conditions => 'base_amount < 0'}) { find(*args) }
  end
end

class Module
  def memoized_subcollection(pklass, name, conditions=nil)
    class_eval <<-STR
      def #{name}_#{pklass}(reload=false)
        @#{name}_#{pklass} = nil if reload
        @#{name}_#{pklass} ||= #{pklass.to_s.singularize.camelize}.#{name}(#{conditions})
      end
    STR
  end
end

class Asset < ActiveRecord::Base
  has_many :items, :dependent => :destroy_all
  memoized_subcollection(:items, :incoming)
  memoized_subcollection(:items, :outgoing)
end