Rails have to create a "fake" column in model

In my tabel I have:

rating_score => The current score
ratings => The number of ratings which led to the score

I want to create a "fake" column named rating which is (rating_score/ratings) in model. That I can use in my controller to order after and in my view.

How should I create this in my model?

Notice that you cannot have the SQL query order your results by a virtual attribute. What you can do is just define the method like this in your model:

def rating
  rating_scope / ratings
end

and order your resultset in ruby based on the value:

results.sort_by(&:rating)