create scope select top locations, industries

app/controllers/home_controller.rb

@@ -3,18 +3,8 @@ class HomeController < ApplicationController
     @total_jobs = Job.count
     @locations = Location.all
     @industries = Industry.all
-    @jobs = Job.order(created_at: :desc).limit(6)
-    @top_cities = list_top_of(@locations, 9)
-    @top_industries = list_top_of(@industries, 9)
-  end
-
-  private
-
-  def list_top_of(list_object, number)
-    top_object = {}
-    list_object.each do |object|
-      top_object[object.id] = object.jobs.count
-    end
-    top_object.sort_by { |_k, v| v }.reverse.take(number)
+    @jobs = Job.order(created_at: :desc).limit(Job::NUMBER_LATEST_JOB)
+    @top_cities = Location.top_locations(9)
+    @top_industries = Industry.top_industries(9)
   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) }
+
   has_and_belongs_to_many :jobs
 end

app/models/job.rb

 class Job < ApplicationRecord
+  NUMBER_LATEST_JOB = 6
+
   belongs_to :company
   has_many :applied_jobs
   has_many :histories

app/models/location.rb

 class Location < ApplicationRecord
-  CITY_VIETNAM_NUMBER = 70.freeze
+  scope :top_locations, ->(number) { joins(:jobs).group(:location_id).order(Arel.sql('count(jobs.id) DESC')).take(number) }
+
+  CITY_VIETNAM_NUMBER = 70
 
   has_many :locations_jobs
   has_many :jobs, through: :locations_jobs

app/views/home/_city.html.erb

-<% location = Location.find_by(id: object[0]) %>
 <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'><%= object[1] %> Jobs</p>
+      <p class='card-text'><%= location.jobs.size %> Jobs</p>
     <% end %>
   </div>
 </div>

app/views/home/_industry.html.erb

-<% industry = Industry.find_by(id: object[0]) %>
 <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'><%= object[1] %> Jobs</p>
+      <p class='card-text'><%= industry.jobs.size %> Jobs</p>
     <% end %>
   </div>
 </div>

app/views/home/index.html.erb

@@ -16,14 +16,14 @@
 <div id='top-city' class='my-4 text-center'>
   <h1>Top Cities</h1>
   <div class='row'>
-    <%= render partial: 'home/city', collection: @top_cities, as: :object %>
+    <%= render partial: 'home/city', collection: @top_cities, as: :location %>
   </div>
   <a href='#'>See more...</a>
 </div>
 <div id='top-industry' class='my-4 text-center'>
   <h1>Top Industries</h1>
   <div class='row'>
-    <%= render partial: 'home/industry', collection: @top_industries, as: :object %>
+    <%= render partial: 'home/industry', collection: @top_industries, as: :industry %>
   </div>
   <a href='#'>See more...</a>
 </div>