Question

I’ve decided to build my newest site using Rails 3. This is my first experience with Rails and wanted to get the communities opinion on how to do the following scenario.

I have the following models created: Item, Rating, User

I would like the app to work as:

1) Item has many Ratings
2) User can submit many Ratings – Only one user submitted rating per item
3) Specific rating can can only have one Item and one User

Based on this I want to be able to:

1) Show all ratings for an item
2) Show all items rated by a particular user

Seems simple enough. Any help or direction is appreciated greatly.

Answer 1

I would use Polymorphic association:

# 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

With this your User can rate different Items, but only once per Item.

To implement this you’d need rateable_id and rateable_type fields in your ratings table. Plus, off course, user_id and rating_score or something.

The great advantage is that you are able to add as much rateables as you wish. If, for example, you want to rate a Song model, then you can simply implement it like this:

# file: app/models/song.rb
class Song < ActiveRecord::Base
  has_many :ratings, :as => :rateable
end

To show ratings for an Item: item.ratings
To show all items rated by a User: user.rated_items

P.S. I am not good in English grammar, so correct me if have misspelled rateable
P.P.S. this implementation is untested, I wrote it straight out of my head, so there’s no guarantee it will work 100% 🙂

Good luck!