Initializing a Module mixed in to a Model

Question

Hi,

I have this:

class Bullet < ActiveRecord::Base  
  include StagedVersionMethods
  ...
end

And this

module StagedVersionMethods     
  def initialize
    puts self.bullet_id
  end
end

When I create an instance of Bullet, the modules initialize method fires, but I get an ActiveRecord error: ...activerecord-2.2.2/lib/active_record/attribute_methods.rb:268:in `read_attribute'

My intent is to initialize an instance variable for which I need the primary key value of the record I'm mixing into. Other methods in the module will then work with this instance variable.

The module included() callback does not fit the task either, because self, in that context, is the Module not the AR record.

How should this be approached?

Thanks

Answer 1

If you define initialize like:

def initialize(*atts)
  super(*atts)
  puts self.bullet_id
end

then I think it will do what you want as it will set up the object correctly for you using the ActiveRecord initialization first. However, I'm not sure how robust that approach is for what you're trying to achieve. It might be more appropriate to create this instance variable when it is accessed rather than when the object is initialized.

It's kind of hard to say without knowing what you want the instance variable to do though.

Answer 2

Overiding the initializer on ActiveRecord can have strange side effects that prove difficult to debug, so it's not recommended. The recommended approach would be to use the :after_initialize callback that ActiveRecord provides instead. You can still mix this behaviour in via a module...

module MyCleverMixin  

  def after_initialize
    puts "I'm Initializing!"
  end

end


class MyModel < ActiveRecord

  include MyCleverMixin

end