Question

I have two models: School and Review.

The School model looks like this: {ID, name, city, state}

The Review model looks like this: {ID, content, score, school_id}

How do I list the top ten schools based on the score from the review model?

I thought maybe a method in the school-model, with something like this:

class School < ActiveRecord::Base
 def top_schools
   @top_schools = School.limit(10)
   ...
 end
end

And then loop them in a <li> list:

<div>
 <ul>
   <% @top_schools.each do |school| %>
      <li>school.name</li>
   <%end>
 </ul>
</div>

But, I dont really know how to finish the top_schools method.

Answer 1

You should make an average of reviews of each school.

The SQL query if you are running with MySQL should be something like:

SELECT schools.* FROM schools 
JOIN reviews ON reviews.school_id=schools.id 
GROUP BY schools.id
ORDER BY AVG(reviews.score) DESC
LIMIT 10

Translated in Rails:

In your School model:

scope :by_score, :joins => :reviews, :group => "schools.id", :order => "AVG(reviews.score) DESC"

In your controller:

@top_schools = School.by_score.limit(10)

The choice not to include the limitation in scope, can be more flexible and allow the display of 5 or 15.

I have only tested MySQL request. I am not sure on my rails translation.