Add functionality to set default live video URL

A new method has been added to the `CoursesController` which allows admins to fill default live video URLs for online lectures that don't have one. This feature is accessible via a button on the courses admin page. The routing for this new action has also been set up.

app/controllers/admin/courses_controller.rb

@@ -1,9 +1,13 @@
 module Admin
   class CoursesController < Admin::ApplicationController
     def renumber_lectures
-      course = Course.find(params[:id])
-      course.renumber_lectures!
-      redirect_to admin_course_url(course), notice: "Lectures renumbered!"
+      requested_resource.renumber_lectures!
+      redirect_to admin_course_url(requested_resource), notice: "Lectures renumbered"
+    end
+
+    def fill_in_default_live_video_url
+      requested_resource.fill_in_default_live_video_url!
+      redirect_to admin_course_url(requested_resource), notice: "Filled in default live video URL"
     end
 
     # Overwrite any of the RESTful controller actions to implement custom behavior

app/models/course.rb

@@ -87,6 +87,6 @@ class Course < ApplicationRecord
 
   def fill_in_default_live_video_url!
     raise "No default live video URL set" if self.default_live_video_url.nil?
-    lectures.where(live_video_url: nil).update_all!(live_video_url: self.default_live_video_url)
+    lectures.where(live_video_url: nil).update_all(live_video_url: self.default_live_video_url)
   end
 end

app/views/admin/course/_actions.html.erb

@@ -3,3 +3,9 @@
       [namespace, page.resource, :renumber_lectures],
       class: "button",
     ) if accessible_action?(page.resource, :renumber_lectures) %>
+
+<%= link_to(
+      "Fill in default live video URL",
+      [namespace, page.resource, :fill_in_default_live_video_url],
+      class: "button",
+    ) if accessible_action?(page.resource, :fill_in_default_live_video_url) && page.resource.default_live_video_url.present? %>

config/routes.rb

@@ -9,6 +9,7 @@ Rails.application.routes.draw do
     root to: "courses#index"
 
     get '/courses/:id/renumber_lectures', to: 'courses#renumber_lectures', as: :course_renumber_lectures
+    get '/courses/:id/fill_in_default_live_video_url', to: 'courses#fill_in_default_live_video_url', as: :course_fill_in_default_live_video_url
   end
 
   root controller: :attendance_tracker, action: :index