Question

I have two models:

Program < ActiveRecord::Base
  has_many :events

  def federal_financing
    events.sum(&:federal_financing)
  end

  def regional_financing
    events.sum(&:regional_financing)
  end

  def local_financing
    events.sum(&:local_financing)
  end
end

Event < ActiveRecord::Base
  belongs_to :program
  # events table have this decimal fields: federal_financing, local_financing, regional_financing
end

Always if I call one of these three methods I’m calling another ones. So I want to avoid of loading events each time I call any of these methods. Current solution now is to define

def after_initialize
  @all_events = events
end

and use @all_events instead of events in methods. BUT I do not want to load events when object loads – I want “cache” events only if any of these three methods was called and other methods should use cached version of events.

Answer 1

I believe you can use the following to load events just once per program:

Program < ActiveRecord::Base
  has_many :events

  def federal_financing
    all_events.sum(&:federal_financing)
  end

  def regional_financing
    all_events.sum(&:regional_financing)
  end

  def local_financing
    all_events.sum(&:local_financing)
  end

  def all_events
    # if @events is not initialized yet or is nil or is false, 
    #    self.events will be loaded. otherwise @events will remain unchanged.
    @events ||= self.events 
  end
end