refactored queries

app/jobs/featured_quiz_mail_scheduler_job.rb

@@ -3,7 +3,7 @@ class FeaturedQuizMailSchedulerJob < ApplicationJob
   queue_as :default
 
   def perform(quiz)
-    user_emails = User.where.not(id: QuizRunner.where(quiz_id: quiz.id).pluck(:user_id)).pluck(:email)
+    user_emails = User.where.not(id: QuizRunner.where(quiz_id: quiz.id).select(:user_id)).pluck(:email)
     FeaturedQuizMailer.with(emails: user_emails, quiz: quiz).featured_quiz_email.deliver_later if user_emails.present?
   end
 

app/mailers/welcome_user_mailer.rb

@@ -1,6 +1,8 @@
 class WelcomeUserMailer < ApplicationMailer
+
   def welcome_user_mail
     @user = params[:user]
     mail(to: @user.email, subject: 'Welcome new user!')
   end
+
 end

app/models/comment.rb

@@ -12,6 +12,8 @@ class Comment < ApplicationRecord
 
   scope :published, -> { where(published: true) }
 
+  scope :on_quizzes, -> { where(commentable_type: 'Quiz') }
+
   def publish
     update_column(:published, true)
   end

app/services/quizathon/stats_manager.rb

@@ -2,7 +2,7 @@ module Quizathon
 
   class StatsManager
 
-    attr_accessor :user_with_most_quiz, :highest_rated_quiz, :highest_scoring_participant, :quizzes_of_highest_scoring_participant, :commenting_user, :quiz_users_count_hash
+    attr_accessor :user_with_most_quiz, :highest_rated_quiz, :highest_scoring_participant, :commenting_user, :quizzes_with_participants_count
 
     def initialize(from, to)
       @from = from || 1.month.ago
@@ -21,29 +21,23 @@ def fetch_stats
     private
 
     def fetch_user_with_most_quiz
-      user_id = QuizRunner.between(@from, @to).select(:user_id, 'count(*) AS quiz_count').group(:user_id).order(quiz_count: :desc).first.user_id
-      @user_with_most_quiz = User.find_by_id(user_id)
+      @user_with_most_quiz = QuizRunner.between(@from, @to).select(:user_id, 'count(*) AS quiz_count').group(:user_id).order(quiz_count: :desc).first.user
     end
 
     def fetch_highest_rated_quiz
-      quiz_id = Rating.select(:quiz_id, 'SUM(value) as total_rating').group(:quiz_id).order(total_rating: :desc).first.quiz_id
-      @highest_rated_quiz = Quiz.find_by_id(quiz_id)
+      @highest_rated_quiz = Rating.select(:quiz_id, 'SUM(value) as total_rating').group(:quiz_id).order(total_rating: :desc).first.quiz
     end
 
     def fetch_highest_scoring_participant(time_range)
-      user_id = QuizRunner.select(:user_id, 'SUM(score) AS total_score').group(:user_id).order(total_score: :desc).first.user_id
-      @highest_scoring_participant = User.find_by_id(user_id)
-      @quizzes_of_highest_scoring_participant = @highest_scoring_participant.quizzes.where(id: QuizRunner.where(created_at: time_range).pluck(:quiz_id))
+      @highest_scoring_participant = User.includes(:quizzes).joins(:quiz_runners).select(:id, :first_name, :last_name, 'SUM(score) AS total_score').where('quiz_runners.created_at': time_range).group(:id).order(total_score: :desc).first
     end
 
     def fetch_commenting_user(time_range, min_no_of_quizzes_commented)
-      user_id = Comment.where(created_at: time_range, commentable_type: 'Quiz').select(:user_id, 'COUNT (DISTINCT commentable_id) as quizzes_count').group(:user_id).having('COUNT (DISTINCT commentable_id) >= ?', min_no_of_quizzes_commented).order(quizzes_count: :desc).first&.user_id
-      @commenting_user = User.find_by_id(user_id)
+      @commenting_user = User.joins(:comments).where(comments: {commentable_type: 'Quiz', created_at: time_range}).group(:id).having('count(distinct comments.commentable_id) >= ?', min_no_of_quizzes_commented).select('users.*, count(distinct comments.commentable_id) as total_quiz_comment').order(total_quiz_comment: :desc).first
     end
 
     def fetch_quizzes_with_participants_count
-      quiz_users_count_records = QuizRunner.select(:quiz_id, 'COUNT(user_id) AS users_count').group(:quiz_id).order(users_count: :desc)
-      @quiz_users_count_hash = quiz_users_count_records.map { |record| [Quiz.find_by_id(record.quiz_id), record.users_count] }.to_h
+      @quizzes_with_participants_count = Quiz.joins(:quiz_runners).select('quizzes.*', 'COUNT(user_id) AS users_count').group(:id).order(users_count: :desc)
     end
 
   end

app/views/admin/stats/index.html.erb

@@ -21,7 +21,7 @@
     <br />
     <ul class="list-group">
       <b>Quizzes :</b>
-      <% @stats_manager.quizzes_of_highest_scoring_participant.each do |quiz| %>
+      <% @stats_manager.highest_scoring_participant&.quizzes.each do |quiz| %>
         <li class="list-group-item"><%= quiz.title %></li>
       <% end %>
     </ul>
@@ -37,11 +37,11 @@
       <th class="text-center">Participants count</th>
       <th class="text-center">Revenue generated(Rs.)</th>
     </tr>
-    <% @stats_manager.quiz_users_count_hash.each do |quiz, users_count| %>
+    <% @stats_manager.quizzes_with_participants_count.each do |quiz| %>
       <tr>
         <td class="text-center"><%= quiz.title %></td>
-        <td class="text-center"><%= users_count %></td>
-        <td class="text-center"><%= quiz&.payments&.size.to_i * 5 %></td>
+        <td class="text-center"><%= quiz.users_count %></td>
+        <td class="text-center"><%= quiz.payments.size * 5 %></td>
       </tr>
     <% end %>
   </table>