Refactor code to improve performance

app/controllers/home_controller.rb

@@ -3,7 +3,7 @@ class HomeController < ApplicationController
     @total_jobs = Job.count
     @locations = Location.select(:id, :city)
     @industries = Industry.select(:id, :name)
-    @jobs = Job.order(created_at: :desc).limit(Job::NUMBER_LATEST_JOB)
+    @jobs = Job.includes(:company, :locations).order(created_at: :desc).limit(Job::NUMBER_LATEST_JOB)
     @top_cities = Location.top_locations(9)
     @top_industries = Industry.top_industries(9)
   end

app/controllers/locations_controller.rb

 class LocationsController < ApplicationController
   def index
-    @vn_cities_lists = Location.vietnam
-    @internal_cities_lists = Location.international
+    @vn_cities_lists = Location.vietnam.count_job
+    @internal_cities_lists = Location.international.count_job
   end
 end

app/models/industry.rb

 class Industry < ApplicationRecord
-  scope :top_industries, ->(number) { joins(:jobs)
-                                      .group(:industry_id)
-                                      .order(Arel.sql('count(jobs.id) DESC'))
-                                      .take(number) }
-
+  scope :count_job, -> { joins(:jobs).group(:industry_id).select('industries.*, count(jobs.id) as job_count') }
+  scope :top_industries, ->(number) { count_job.order(Arel.sql('count(jobs.id) DESC')).limit(number) }
   has_and_belongs_to_many :jobs
 end

app/models/location.rb

 class Location < ApplicationRecord
-  scope :top_locations, ->(number) { joins(:jobs)
-                                    .group(:location_id)
-                                    .order(Arel.sql('count(jobs.id) DESC'))
-                                    .take(number) }
-  scope :international, ->{ where(oversea: true) }
-  scope :vietnam, ->{ where(oversea: false) }
-
+  scope :count_job, -> { joins(:jobs).group(:location_id).select('locations.*, count(jobs.id) as job_count') }
+  scope :top_locations, ->(number) { count_job.order(Arel.sql('job_count DESC')).limit(number) }
+  scope :international, -> { where(oversea: true) }
+  scope :vietnam, -> { where(oversea: false) }
+  
   CITY_VIETNAM_NUMBER = 70
 
   has_many :locations_jobs

app/views/industries/_industry.html.erb

-<% if industry.jobs.size.positive? %>
 <div class='col-4 my-2'>
   <div class='card'>
     <%= link_to '#', class: 'card-body text-decoration-none' do %>
       <h5 class='card-title font-weight-bold'><%= industry.name %></h5>
-      <p class='card-text'><%= industry.jobs.size %> Jobs</p>
+      <p class='card-text'><%= industry.job_count %> Jobs</p>
     <% end %>
   </div>
 </div>
-<% end %>

app/views/locations/_city.html.erb

-<% if location.jobs.size.positive? %>
 <div class='col-4 my-2'>
   <div class='card'>
     <%= link_to '#', class: 'card-body text-decoration-none' do %>
       <h5 class='card-title font-weight-bold'><%= location.city %></h5>
-      <p class='card-text'><%= location.jobs.size %> Jobs</p>
+      <p class='card-text'><%= location.job_count %> Jobs</p>
     <% end %>
   </div>
-</div>
-<% end %>
+</div>
\ No newline at end of file

app/views/locations/index.html.erb

@@ -4,11 +4,11 @@
   <ul class='list-group list-group-horizontal'>
     <li class='list-group-item'>
       <a href='#vietnam'>Việt Nam</a>
-      <span class='badge badge-primary badge-pill'><%= @vn_cities_lists.size %></span>
+      <span class='badge badge-primary badge-pill'><%= @vn_cities_lists.length %></span>
     </li>
     <li class='list-group-item'>
       <a href='#international'>International</a>
-      <span class='badge badge-primary badge-pill'><%= @internal_cities_lists.size %></span>
+      <span class='badge badge-primary badge-pill'><%= @internal_cities_lists.length %></span>
     </li>
   </ul>
 </div>