Rails - Validate uniqueness based on another table

Question

I have vote and votedown tables for posts. I can validate uniqueness within the vote and votedown models to ensure that users cant vote or votedown more than once. I'd like to validate uniqueness across the both models so that a user cant votedown a post that theyve already voted up or vice versa. Ive tried the custom validation, userfaved, defined below but its not working.

 class Vote < ActiveRecord::Base

 validates_uniqueness_of :user_id,  :scope => :article_id #allows only one vote

 validate :userfaved

 def userfaved
  if Votedown.where( :user_id => :user_id, :artcle_id => :article_id).any?
      errors.add(:user_id, 'already voted on this') 
  end
 end



class Votedown < ActiveRecord::Base

validates_uniqueness_of :user_id, :scope => :article_id #allows only one votedown

validate :userfaved

def userfaved
    if Vote.where(:user_id=> :user_id, :article_id => :article_id).any?
        errors.add(:user_id, 'already voted on this')
    end
end

Answer 1

It looks like there's a bug in your validation: the values in the hash you're passing to where are symbols. Change it to the following and it should work:

Votedown.where( :user_id => self.user_id, :article_id => self.article_id).any?

But I think there's a simpler way to do this. Could you just have one table Votes and add an attribute to it that records whether it's up or down? That would make your uniqueness check very simple. If you really want separate classes for it, you could use single table inheritance: have a votes table, a superclass Vote, and two subclasses, VoteUp and VoteDown.