event.rb

class Event < ActiveRecord::Base
  extend ActiveSupport::Memoizable

  cattr_accessor :year

  belongs_to :program
  has_many :financing_periods, :dependent => :destroy

  def current_period
    financing_periods.current(@@year).last(:include => [:plain_financings, { :named_financings => :district }])
  end

  def planned_federal_financing
    current_period ? current_period.planned_federal_financing : 0.0
  end

  memoize :current_period,
          :planned_federal_financing
end

financing_period.rb

class FinancingPeriod < ActiveRecord::Base
  extend ActiveSupport::Memoizable

  belongs_to :event

  has_many :financings, :dependent => :destroy

  named_scope :current, lambda { |year| {:order => :date, :conditions => ['YEAR(date) = ?', year || Time.now.year.to_int] } }

  def planned_federal_financing
    financings.sum(&:planned_federal_financing)
  end

  memoize :planned_federal_financing
end

program.rb

class Program < ActiveRecord::Base
  extend ActiveSupport::Memoizable
  acts_as_tree
  has_many :events
  ...
  def planned_federal_financing
    events.sum(&:planned_federal_financing) + children.sum(&:planned_federal_financing)
  end
  ...
  memoize :planned_federal_financing
end