Implementing sort ASC or DESC in Rails - ruby-on-rails

Question

I am working with an open source school management software, Fedena and I am trying to sort a list of users by their surnames. The software currently shows all users with their first names. I've found these two files to be responsible for showing the information I intend to change.
student_controller.rb
def list_students_by_course
#students = Student.find_all_by_batch_id(params[:batch_id], :order => 'last_name ASC')
render(:update) { |page| page.replace_html 'students', :partial => 'students_by_course' }
end
When I delete the above section of the file, the users names don't show up so I believe this section to be responsible for populating the table with the usernames.
_students_by_course.erb
<div class="students-table">
<table align="center" width="100%" cellpadding="1" cellspacing="1">
<tr class="tr-head">
<td><%= t('sl_no') %></td>
<td><%= t('name') %></td>
<td><%= t('adm_no') %></td>
<td></td>
</tr>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<% #students.each_with_index do |r, i| %>
<tr class="tr-<%= cycle('odd', 'even') %>">
<td class="col-1">
<%= i+1 %>
</td>
<td class="col-2">
<%= link_to r.full_name,:controller => "student", :action => "profile", :id => r.id %>
</td>
<td class="col-1">
<%= r.admission_no %>
</td>
<td class="col-7">
<%= link_to "#{t('view_profile')}", :controller => "student", :action => "profile", :id => r.id %>
</td>
</tr>
<% end %>
</table>
</div>
I have tried changing 'last_name ASC' to 'last_name DESC' but nothing changed.
Any help is appreciated.

Answer 1

You've clarified in the comments that you want not sort order (I take it you've figured that out?) but the format of full name displayed for each instance of a model Student.
It's not hard if traced to the source. Let's start with a view, since that's what we see.
#students.each_with_index do |r, i|
We start a loop, each iteration of which processes an entry r with an index i. Since we're looping on a collection of Students (seems like a valid assumption), r is an instance of Student. The problematic line is:
<%= link_to r.full_name,:controller => "student", :action => "profile", :id => r.id %>
Actually, we should only look at r.full_name since that's what we get as a link label. It's a Student's method. Here it is.
def full_name
"#{first_name} #{middle_name} #{last_name}"
end
You might be wondering where is a second space, since such implementation implies that if middle_name is absent, we'd have two. Look at the source of the page and you'll see that there are actually two! So in order to change how the full name looks, you'll have to modify this method.