How can I cache a calculated column in rails?

Question

I have a tree of active record objects, something like:

class Part < ActiveRecord::Base
  has_many :sub_parts, :class_name => \"Part\"

  def complicat         


        

Answer 1

I suggest using association callbacks.

class Part < ActiveRecord::Base
  has_many :sub_parts,
    :class_name => "Part",
    :after_add => :count_sub_parts,
    :after_remove => :count_sub_parts

  private

  def count_sub_parts
    update_attribute(:sub_part_count, calculate_sub_part_count)
  end

  def calculate_sub_part_count
    # perform the actual calculation here
  end
end

Nice and easy =)