fetch necessary information

app/controllers/users/admins_controller.rb

@@ -16,9 +16,10 @@ class Users::AdminsController < ApplicationController
       user = User.find_by(email: params[:search_user])
       return redirect_to users_admin_path, notice: "User/job not found!" if user.blank?
 
-      user.jobs
+      applied_jobs = user.jobs
+      applied_jobs.page(params[:page]).per(Settings.job.per_page)
     else
-      UserJob.where.not(applied_at: nil).collect { |uj| uj.job }
+      Job.joins(:user_jobs).where.not(user_jobs: { applied_at: nil}).distinct
     end
   end
 end

app/helpers/job_helper.rb

@@ -5,10 +5,6 @@ module JobHelper
   end
 
   def job_applied_at(job)
-    job.user_jobs[0].applied_at
-  end
-
-  def get_all_user
-    User.all
+    job.user_jobs.find_by(user_id: current_user.id).applied_at
   end
 end

app/models/user.rb

@@ -35,4 +35,8 @@ class User < ApplicationRecord
   # :confirmable, :lockable, :timeoutable, :trackable and :omniauthable
   devise :database_authenticatable, :registerable,
          :recoverable, :rememberable, :validatable
+
+  def self.list_emails
+    @emails ||= self.all.pluck(:email)
+  end
 end

app/views/users/admins/index.html.erb

 <h4>Search user's applied jobs:</h4>
 
 <%= form_tag(users_admin_path, method: :get) do |f| %>
-  <%= select_tag :search_user, options_from_collection_for_select(get_all_user, "email", "email", params[:search_user]), include_blank: "Choose user's email" %>
+  <%= select_tag :search_user, options_for_select(User.list_emails, params[:search_user]), include_blank: "Choose user's email" %>
   <%= submit_tag "Search" %>
 <% end %>