snippet.rb

class Rating < ActiveRecord::Base
  belongs_to :user
  belongs_to :rater, :class_name => 'User', :foreign_key => 'rater_id'
  belongs_to :account

  attr_accessible :score, :rater_id, :user_id, :rater, :user

  VALID_SCORES = 1..3

  validates_presence_of :score, :user_id, :rater_id, :account_id
  validates_inclusion_of :score, :in => VALID_SCORES, :message => "must be 1, 2, or 3"
  validates_uniqueness_of :user_id, :scope => :rater_id, :message => 'has already been rated'