post.rb

# create_table :posts do |table|
#   table.string :title, :null => false, :default => ''
#   table.string :body, :null => false, :default => ''
#   table.string :published, :default => false
# end
class Post < ActiveRecord::Base
  attr_accessible :title, :body
  validates_presence_of :title
  validates_presence_of :body, :if => :published?

  def publish(attributes = {})
    self.attributes = attributes
    self.published = true
    save
  end
end