Ruby on Rails 3 Multiple Associations

I have the following associations in place:

class User < ActiveRecord::Base
  has_many :shopping_requests
  has_many :recommendations, :through => :shopping_requests
end


class ShoppingRequest < ActiveRecord::Base
  belongs_to :user
  has_many :recommendations
end


class Recommendation < ActiveRecord::Base
  belongs_to :shopping_request
  has_one :user, :through => :shopping_requests
end

Now I need to add a Compliment class. A user can compliment another user (so I have a user_from_id and a user_to_id). A compliment can be given for either a shopping request and/or a recommendation; and there's no limit (a user can be given several compliments by the same user or other users for any number of shopping requests as well as for recommendations).

I do know to make the Compliment polymorphic but not sure what is the best way to set it up in relation to users/shopping requests/recommendations.

I want to be able to run queries like this:

• user_to_id.compliments (to get all the compliments for the user);
• user_to_id.shopping_request.compliments (to get all that user's compliments for a particular shopping request;
• user_to_id.recommendation.compliments (to get all that user's compliments for a particular recommendation; for this particular query, running user_to_id.shopping_request.recommendation.compliments is fine too);
• user_from_id.compliments (to get all the compliments that a user gave another);
• user_from_id.shopping_request.compliments (to get all the compliments given by this user for a particular shopping_request), etc....

So what is the best way to set up the association for the Compliment class?