example.rb

class Widget < ActiveRecord::Base
  attr_accessible :name, :snippets, :snippets_attributes, :company_id, :hostname, :first_page, :affiliate_id, :item_defaults, :read_only
  has_many :snippets
  has_many :permissions, dependent: :destroy
  has_many :users, through: :permissions
  accepts_nested_attributes_for :snippets
  attr_accessor :read_only

  def read_only
    true
  end

  def attributes
    super.merge({'read_only' => read_only})
  end
end

widget_controller.rb

 def widget
    @hide_nav = true
    @widget = Widget.find_by_url(params[:id])
    @widget = Widget.find_by_id(params[:id]) unless @widget
    @widget.read_only = !current_user.has_role? :admin
    render 'widget' , layout: 'edit_widget'
  end