Multiple counter_cache in Rails model

Question

Hi. I'm learning Rails, and got into a little problem. I'm writing dead simple app with lists of tasks, so models look something like that:

class List < ActiveRecord::Base
  has_many :tasks
  has_many :undone_tasks, :class_name => 'Task',
                          :foreign_key => 'task_id',
                          :conditions => 'done = false'
  # ... some validations
end

Table for List model has columns tasks_counter and undone_tasks_counter.

class Task < ActiveRecord::Base
  belongs_to :list, :counter_cache => true
  # .. some validations
end

With such code there is attr_readonly :tasks_counter for List instances but I would like to have a counter for undone tasks as well. Is there any way of having multiple counter cached automagically by Rails.

So far, I've managed to create TasksObserver that increments or decrements Task#undone_tasks_counter, but maybe there is a simpler way.

Answer 1

I'm not aware of any "automagical" method for this. Observers seems good for this, but I personally prefer using callbacks in model (before_save, after_save).