How do you validate uniqueness of a pair of ids in Ruby on Rails?

Question

Suppose the following DB migration in Ruby:

    create_table :question_votes do |t|
      t.integer :user_id
      t.integer :question_id
      t.integer :vote

          


        

Answer 1

From RailsGuides. validates works too:

class QuestionVote < ActiveRecord::Base
  validates :user_id, :uniqueness => { :scope => :question_id }
end