Question

I am trying to use the link_to feature to link one view to another.

The view i am calling link_to is app/views/instructors/show.html.erb and that snippet of code looks like this (namely, the second to last line of it)

<% provide(:title, @instructor.login) %>
<% courses = Course.where(:instructor_ID => @instructor.id) %>
    <div class="span2">
      <h1 align=center ><%= @instructor.login %></h1>
      <%= link_to "Add course", new_course_path(:instructor_ID\
                => @instructor.id), :class => "btn" %>
        <br>
        <br>
        <%= link_to "Remove course", delete_course_path(courses), :class => "btn"%>
    </div>

The view I am trying to link to is is app/views/courses/show_all.html.erb and looks like this:

<% @courses.each do |course| %>
  <tr>
    <td><%= course.course_name %></td>
    <td><%= course.instructor_ID %></td>
    <td><%= link_to 'Show', course %></td>
    <td><%= link_to 'Edit', edit_course_path(course) %></td>
    <td><%= link_to 'Destroy', course, :method => :delete, :data => { :confirm => 'Are you sure?' } %></td>
  </tr>

delete_course_path routes to app/views/courses/show_all.html.erb shown above. When I try the code above, I get the following error:

undefined method `each’ for nil:NilClass

At this line:

<% @courses.each do |course| %>

Any ideas what i’m missing in my link_to?

Answer 1

In your show_all action, you should define a @courses instance variables. This is

<% courses = Course.where(:instructor_ID => @instructor.id) %>

not passed to show_all.html.erb.

An instance variables is a variable passed from action of controller to the view corresponding.

I suppose when you show page of instructor, your route will like this: /instructors/:id, so maybe in your show_all action of instructor controller, you need something like:

def show_all
  @courses = Course.where(instructor_ID: params[:id])
  render 'courses/show_all'
end