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

The best way is to use both, since rails isn't 100% reliable when uniqueness validation come thru.

You can use:

  validates :user_id, uniqueness: { scope: :question_id }

and to be 100% on the safe side, add this validation on your db (MySQL ex)

  add_index :question_votes, [:user_id, :question_id], unique: true

and then you can handle in your controller using:

  rescue ActiveRecord::RecordNotUnique

So now you are 100% secure that you won't have a duplicated value :)