Question

class Task < ActiveRecord::Base
  attr_accessible :due_date, :text

  def self.this_week
    where(:due_date => Date.today.beginning_of_week..Date.today.end_of_week)
  end
end

class Important < ActiveRecord::Base
  attr_accessible :email

  has_one :task, :as => :taskable, :dependent => :destroy

  delegate this_week, :to => :task
end

So far this delegate is not working as expected, when I try Important.this_week. I get an error saying there is no method this_week defined for class…

Any ideas? Can I even delegate to a class method like this? I may have another class or two extending Task in this way, so I’m curious how this works in a way that doesn’t duplicate a bunch of code to each implementing class.

Answer 1

You’re picking up the ActiveSupport delegation core extension. The delegate helper defines an instance method for the current class so that instances of it delegate calls to some variable on that instance.

If you want to delegate at the class level, you need to open up the singleton class and set up the delegation there:

class Important < ActiveRecord::Base
  attr_accessible :email

  has_one :task, :as => :taskable, :dependent => :destroy

  class << self
    delegate :this_week, :to => :task
  end
end

But this assumes that Important.task is a reference to the Task class (which it is not)

Rather than relying on the delegation helper, which is just going to make your life difficult, I’d suggest explicit proxying here:

class Important < ActiveRecord::Base
  attr_accessible :email

  has_one :task, :as => :taskable, :dependent => :destroy

  class << self
    def this_week(*args, &block)
      Task.this_week(*args, &block)
    end
  end
end