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copied!<p>I would use Polymorphic association:</p> <pre><code># file: app/models/item.rb class Item < ActiveRecord::Base has_many :ratings, :as => :rateable end # file: app/models/user.rb class User < ActiveRecord::Base has_many :ratings has_many :rated_items, :through => :ratings, :source => :rateable, :source_type => "Item" end # file: app/models/rating.rb class Rating < ActiveRecord::Base belongs_to :user belongs_to :rateable, :polymorphic => true validates_uniqueness_of :user_id, :scope => :rateable end </code></pre> <p>With this your User can rate different Items, but only once per Item. </p> <p>To implement this you'd need <code>rateable_id</code> and <code>rateable_type</code> fields in your <code>ratings</code> table. Plus, off course, <code>user_id</code> and <code>rating_score</code> or something.</p> <p>The great advantage is that you are able to add as much <code>rateables</code> as you wish. If, for example, you want to rate a <code>Song</code> model, then you can simply implement it like this:</p> <pre><code># file: app/models/song.rb class Song < ActiveRecord::Base has_many :ratings, :as => :rateable end </code></pre> <p>To show ratings for an <code>Item</code>: <code>item.ratings</code> To show all items rated by a <code>User</code>: <code>user.rated_items</code></p> <p>P.S. I am not good in English grammar, so correct me if have misspelled <code>rateable</code><br> P.P.S. this implementation is untested, I wrote it straight out of my head, so there's no guarantee it will work 100% :)</p> <p>Good luck!</p>

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