```ruby
class Vote < ActiveRecord::Base

  belongs_to :user
  belongs_to :response

end
```

Resolve merge conflict by keeping validations that prevent users from voting on more than one response per question.
user
```ruby
class Vote < ActiveRecord::Base

  belongs_to :user
  belongs_to :response

  validates :user, uniqueness: {  scope: :response,
                                  message: "User can only vote on this response once."}
end
```
assistant