Create a variable in controller to order by - ruby-on-rails

Question

I have a form where a 3 of the user inputs have numbers (week1,2 and 3). I'd like to create a variable in my controller that would add the fields together.
i.e score = student.week1 + student.week2 + student.week3
I would then like to order the students on the students.index.html.erb page by the highest score. Part of the issue is my index page does not have a student.id until i go to the show or edit page etc
My student model:
class Student < ApplicationRecord
belongs_to :user
def to_param
"#{id}-#{fname.parameterize}-#{lname.parameterize}"
end
end
My Student controller
class StudentsController < ApplicationController
def index
#pagy, #students = pagy(Student.all, page: params[:page], items: 16)
#students.order([:week1_score] + [:week2_score] + [:week3_score])
end
def new
#student = Student.new
end
end
I have tried creating a
def score
week1_score = #student.week1_score
week2_score = #student.week2_score
week3_score = #student.week3_score
week1_score + week2_score + week3_score
end
But i'm guessing the user_id is whats holding me back. Aside from the ordering, i'd still like to know the score of each student. Thanks

Answer 1

You're approaching the problem completely wrong from the get go.
If the students table has the columns week1_score, week2_score, week3_score you should add them together in situ so that you can order the records in the database.
class StudentsController < ApplicationRecord
...
def index
#students = Student.select(
'students.*',
'(students.week1_score + students.week2_score + students.week3_score) AS total_score'
).order(:total_score)
end
...
end
Your attempt:
.order([:week1_score] + [:week2_score] + [:week3_score])
is actually a really bad equivalent to calling:
.order(:week1_score, :week2_score, :week3_score)
This will order by the three columns - not by the total.