From 5014d7bbb4852a9c2f3cc58ac0eb6ebc5ac77649 Mon Sep 17 00:00:00 2001
From: Tim Schroeder <t.schroeder@itc.rwth-aachen.de>
Date: Fri, 16 Jun 2023 18:07:51 +0200
Subject: [PATCH] MDL-78488 question bank: don't load statistics when they are
 disabled

---
 .../statistics/statistics_bulk_loader.php     |  9 +++++++
 .../statistics_bulk_loader_test.php           | 27 +++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/question/classes/local/statistics/statistics_bulk_loader.php b/question/classes/local/statistics/statistics_bulk_loader.php
index 60ad643a255..3191ac8e45e 100644
--- a/question/classes/local/statistics/statistics_bulk_loader.php
+++ b/question/classes/local/statistics/statistics_bulk_loader.php
@@ -43,6 +43,15 @@ class statistics_bulk_loader {
      * @return float[][] if a value is not available, it will be set to null.
      */
     public static function load_aggregate_statistics(array $questionids, array $requiredstatistics): array {
+        // Prevent unnecessary statistics calculations.
+        if (empty($requiredstatistics)) {
+            $aggregates = [];
+            foreach ($questionids as $questionid) {
+                $aggregates[$questionid] = [];
+            }
+            return $aggregates;
+        }
+
         $places = self::get_all_places_where_questions_were_attempted($questionids);
 
         // Set up blank two-dimensional arrays to store the running totals. Indexed by questionid and field name.
diff --git a/question/tests/local/statistics/statistics_bulk_loader_test.php b/question/tests/local/statistics/statistics_bulk_loader_test.php
index 09141bdab74..d0a4d49e956 100644
--- a/question/tests/local/statistics/statistics_bulk_loader_test.php
+++ b/question/tests/local/statistics/statistics_bulk_loader_test.php
@@ -553,4 +553,31 @@ class statistics_bulk_loader_test extends advanced_testcase {
         $this->assertEqualsWithDelta($expectedaveragediscriminationindex[3],
             $stats[$questions[4]->id]['discriminationindex'], self::PERCENT_DELTA);
     }
+
+    /**
+     * Test with question statistics disabled
+     */
+    public function test_statistics_disabled(): void {
+        $this->resetAfterTest();
+
+        // Prepare some quizzes and attempts. Exactly what is not important to this test.
+        $quiz1attempts = [$this->generate_attempt_answers([1, 0, 0, 0])];
+        $quiz2attempts = [$this->generate_attempt_answers([1, 1, 1, 1])];
+        [, , $questions] = $this->prepare_and_submit_quizzes($quiz1attempts, $quiz2attempts);
+
+        // Prepare some useful arrays.
+        $expectedstats = [
+            $questions[1]->id => [],
+            $questions[2]->id => [],
+            $questions[3]->id => [],
+            $questions[4]->id => [],
+        ];
+        $questionids = array_keys($expectedstats);
+
+        // Ask to load no statistics at all.
+        $stats = statistics_bulk_loader::load_aggregate_statistics($questionids, []);
+
+        // Verify we got the right thing.
+        $this->assertEquals($expectedstats, $stats);
+    }
 }