avoiding code duplication in Rails 3 models - ruby-on-rails-3

Question

I'm working on a Rails 3.1 application where there are a number of different enum-like models that are stored in the database. There is a lot of identical code in these models, as well as in the associated controllers and views. I've solved the code duplication for the controllers and views via a shared parent controller class and the new view/layout inheritance that's part of Rails 3.
Now I'm trying to solve the code duplication in the models, and I'm stuck. An example of one of my enum models is as follows:
class Format < ActiveRecord::Base
has_and_belongs_to_many :videos
attr_accessible :name
validates :name, presence: true, length: { maximum: 20 }
before_destroy :verify_no_linked_videos
def verify_no_linked_videos
unless self.videos.empty?
self.errors[:base] << "Couldn't delete format with associated videos."
raise ActiveRecord::RecordInvalid.new self
end
end
end
I have four or five other classes with nearly identical code (the association declaration being the only difference). I've tried creating a module with the shared code that they all include (which seems like the Ruby Way), but much of the duplicate code relies on ActiveRecord, so the methods I'm trying to use in the module (validate, attr_accessible, etc.) aren't available. I know about ActiveModel, but that doesn't get me all the way there.
I've also tried creating a common, non-persistent parent class that subclasses ActiveRecord::Base, but all of the code I've seen to accomplish this assumes that you won't have subclasses of your non-persistent class that do persist.
Any suggestions for how best to avoid duplicating these identical lines of code across many different enum models?

Answer 1

I found a solution to the code sharing for Rails 3 models, so thought I'd share it with others. It turns out ActiveModel does have everything I need (so far, at least). I created an Enum module using ActiveSupport::Concern, ActiveModel::Validations, and ActiveModel::MassAssignmentSecurity, and I include the module in each of my enum models:
module Enum
extend ActiveSupport::Concern
include ActiveModel::Validations
include ActiveModel::MassAssignmentSecurity
included do
attr_accessible :name
validates :name, presence: true, length: { maximum: 20 }
before_destroy :verify_no_linked_videos
private
def verify_no_linked_videos
unless self.videos.empty?
self.errors[:base] << "Couldn't delete object with associated videos."
raise ActiveRecord::RecordInvalid.new self
end
end
end
end
The way the Rails 3 team pulled out the non-database code from ActiveRecord into ActiveModel really is pretty slick! The following links helped solidify my understanding of how to use this stuff:
http://www.fakingfantastic.com/2010/09/20/concerning-yourself-with-active-support-concern/
http://asciicasts.com/episodes/237-dynamic-attr-accessible