[Beginning Rails 3] Listing 5-17. The Article model in app/models/article.rb

article.rb

class Article < ActiveRecord::Base
  validates :title, :presence => true
  validates :body, :presence => true

  belongs_to :user
  has_and_belongs_to_many :categories
  has_many :comments
  
  def long_title
    "#{title} - #{published_at}"
  end
end