Speed up external user statistics

app/controllers/external_users_controller.rb

@@ -14,9 +14,53 @@ class ExternalUsersController < ApplicationController
     authorize!
   end
 
+  def working_time_query
+    """
+    SELECT user_id,
+           exercise_id,
+           max(score) as maximum_score,
+           count(id) as runs,
+           sum(working_time_new) AS working_time
+    FROM
+      (SELECT user_id,
+              exercise_id,
+              score,
+              id,
+              CASE
+                  WHEN working_time >= '0:30:00' THEN '0'
+                  ELSE working_time
+              END AS working_time_new
+       FROM
+         (SELECT user_id,
+                 exercise_id,
+                 max(score) AS score,
+                 id,
+                 (created_at - lag(created_at) over (PARTITION BY user_id, exercise_id
+                                                     ORDER BY created_at)) AS working_time
+          FROM submissions
+          WHERE user_id = #{@user.id}
+            AND user_type = 'ExternalUser'
+          GROUP BY exercise_id,
+                   user_id,
+                   id) AS foo) AS bar
+    GROUP BY user_id,
+             exercise_id;
+    """
+  end
+
   def statistics
     @user = ExternalUser.find(params[:id])
     authorize!
+
+    statistics = {}
+
+    ActiveRecord::Base.connection.execute(working_time_query).each do |tuple|
+      statistics[tuple["exercise_id"].to_i] = tuple
+    end
+
+    render locals: {
+      statistics: statistics
+    }
   end
 
 end

app/views/external_users/statistics.html.slim

@@ -10,9 +10,9 @@ h1 = t('.title')
           th.header = t(title)
     tbody
       - exercises.each do |exercise|
-        - submissions = @user.submissions.where(:exercise_id => exercise.id, :cause => ['submit', 'run'])
+        - if statistics[exercise.id] then stats = statistics[exercise.id] else stats = {"working_time" => 0, "runs" => 0, "score" => 0}
         tr
           td = link_to exercise, controller: "exercises", action: "statistics", external_user_id: @user.id, id: exercise.id
-          td = submissions.maximum(:score) or 0
+          td = stats["maximum_score"] or 0
-          td = submissions.count
+          td = stats["runs"] or 0
-          td = exercise.average_working_time_for_only(@user.id) or 0
+          td = stats["working_time"] or 0

config/locales/de.yml

@@ -269,7 +269,7 @@ de:
       title: Statistiken für Externe Benutzer
       exercise: Übung
       score: Bewertung
-      runs: Versuche
+      runs: Abgaben
       worktime: Arbeitszeit
   files:
     roles:

config/locales/en.yml

@@ -269,7 +269,7 @@ en:
       title: External User Statistics
       exercise: Exercise
       score: Score
-      runs: Runs
+      runs: Submissions
       worktime: Working Time
   files:
     roles: