Rails: How do I check a polymorphic association?

I have the follow model setup:

class Favorite < ActiveRecord::Base
  belongs_to :favoritable, :polymorphic => true
  belongs_to :us开发者_开发技巧er
end

class Photo < ActiveRecord::Base
  belongs_to :user
  has_many :favorites, :as => :favoritable
end

class User < ActiveRecord::Base
  has_many :photos
end

And that Favorite model has favoritable_id and favoritable_type` fields.

What I ultimately want to do is check and see if a User has already marked a photo as a favorite.

I'm able to create the database record without issue...it's the checking to see if that user already has favorited the photo (or other data type) that I'm having issues with.

I could obviously do some sort of raw SQL query to get it, but seems like there's gotta be a more "standard" way of doing it.

I'm running Rails 3.0.3.

---

you can add two other associations in the User model and a method that checks if the photo is favorite :

has_many :favorites
has_many :favorites_photos, :through => :favorites, :source => :favoritable, :source_type => 'Photo'

def photo_favorite?(photo)
  favorites_photos.exists?(photo.id)
end

or more simply just by adding this method to the Photo model :

def favorite_for?(user)
  favorites.exists?(:user_id => user.id)
end

I did not tested it, but I think it should work.