Rails Mongoid model/view calculation

Question

I need to do some calculation through a view on a few models. Example:

class Teacher
  include Mongoid::Document

  has_many :students
end

class Student
  include Mongoid::Document
  belogns_to :teacher

  field gold_stars, type: Integer
  field silver_stars, type: Integer
  field bronze_stars, type: Integer
end

Let's say on the Teacher's view I need to aggregate the number of gold_stars, silver_stars and bronze_stars. What is the cleanest way to aggregate the values in the view? I'm guessing I would use a after_update callback but I'm not sure if there is a nicer way.

UPDATE

What I want is for the Teacher to display how many gold stars all his students have in total, then silver, then bronze.

you want to aggregate number of stars for all the students belongs_to a teacher or total stars of students?? — abhas, Oct 05 '12 at 04:06

score 1 · Accepted Answer · answered Oct 05 '12 at 05:25

1

here is the solution

teacher = Teacher.first
gold_stars = Student.where(:teacher_id => teacher.id).sum(:gold_stars)
silver_stars = Student.where(:teacher_id => teacher.id).sum(:silver_stars)
bronze_stars = Student.where(:teacher_id => teacher.id).sum(:bronze_stars)

answered Oct 05 '12 at 05:25

abhas

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Elegant I like thanks. Do you think this belongs in a virtual attribute on Teacher class? – GTDev Oct 05 '12 at 05:51

Rails Mongoid model/view calculation

1 Answers1