Make a ASC and Desc link work on my ruby on rails

Question

I added two links that say ASC and Desc but i cant get them to work. I made the links sort by ascending and descending but it isn't doing anything. Any help? (index.html.erb)

<p id="notice"><%= notice %></p>

<% @grades = Grade.all %>

<h1>Grades</h1>
Grade Sort By:
<%= link_to "ASC", grades_path(sort_by: 'asc')%>
<%= link_to "DESC", grades_path(sort_by: 'desc')%>
<table>
  <thead>
  
    <tr>
    <th><%= link_to "Student", sort: " student_id"%> </th>
    <th><%= link_to "Student name", sort: "student_name"%> </th>
    <th><%= link_to "Student grade", sort:  "student_grade"%> </th>
    <th colspan="3"></th>

  </tr>
  </thead>

(grades_controller.rb)

class GradesController < ApplicationController
  before_action :set_grade, only: [:show, :edit, :update, :destroy]

  # GET /grades
  def index
    if !user_signed_in?
      redirect_to user_session_path
    end

    @grades = Grade.all
    @grades = @grades.order(student_grade: params[:sort_by]) if params[:sort_by].present?

  end

Answer 1

I believe you should do something like

if params[:sort_by]
  @grades = Grade.joins(:student).order( {"students.name": :params[:sort_by]} ) 
else
 @grades = Grade.all
end

and if that does not work go for

if params[:sort_by] == 'asc'
  @grades = Grade.joins(:student).order("students.name ASC") 
elsif params[:sort_by] == 'desc'
  @grades = Grade.joins(:student).order("students.name DESC") 
else
 @grades = Grade.all
end

Edit: I just noticed the body part of the table is missing. You are not populating the rows of the table by iterating over @grades. Something like

  <tbody>
    <% @grades.each do |grade| %>
      <tr class = "center">
        <td><%= grade.student.name %></td>
        <td>......</td>
        <td>......</td>
      </tr>
    <% end %>
  </tbody>