HABTM Association in Rails 3.0

# Extend ActiveRecord::Base with this method using your preferred technique.
    def self.anaf_habtm(association, &block)
      class_eval do
        # Define a proc that will look up the (potentially) existing object
        finder = proc {|id| association.to_s.singularize.camelize.constantize.where(:id=>id).first
        }
 
        # Define a proc that will set the association collection
        set_collection = proc {|me, coll| me.send("#{association.to_s.tableize}=", coll)}
        # Define the actual association setter.
        define_method "#{association.to_s.tableize}_attributes=", lambda{|attributes_for_association|
          coll = []
 
          attributes_for_association.each_value do |params|
            next if params["_destroy"] == "1"
            obj = finder.call(params["id"]) if params.has_key?("id")
            params.extend(HashExtension)
            # ActiveRecord::Base.attributes=() doesn't like extra parameters.
            coll << block.call(params.copy_without_destroy, obj)
          end
          set_collection.call(self, coll)
        }
      end
    end
 
 
    # Inside your model definition, define your association as such:
class Person < ActiveRecord::Base
  has_and_belongs_to_many :web_sites, :autosave => :true, :uniq => true
  has_and_belongs_to_many :recreational_organizations, :autosave => :true, :uniq => true
 
  # This one has some extra parameters that will be saved to the association
  anaf_habtm(:web_sites) do |params, web_site|
    web_site = web_site ||= WebSite.find_by_url(params["url"])
    web_site.attributes = params
    web_site.save
    web_site
  end
 
  # This one is more simple -- just make a new one if nil was passed in
  anaf_habtm(:recreational_organizations) do |params, org|
    org ||= RecreationalOrganization.new(:name => params["name"])
  end
 
module HashExtension
  def copy_without_destroy
    a = {}
    self.each {|key,val| a[key]=val unless key.to_s == "_destroy"}
    a
  end
end