Question

I have a Course model which has_many reviews. My Review model has a rating field. What I would like is a query to find the top rated courses. I want to do this in the SQL in order to avoid returning all the course objects and then trying to rank and sort them.

Answer 1

You don’t describe how you define “top rated”. It could be that you want the courses with the highest individual ratings:

Course.joins(:reviews).group("courses.id").order("reviews.rating desc")

Or you might want the courses with the highest total ratings:

Course.joins(:reviews).group("courses.id").order("sum(reviews.rating) desc")

Then on each of these you can call first(10) to get the top ten by whichever criteria you want.