From 14574fdb567b6fe4fa5e9200a0a1fe68bb614a43 Mon Sep 17 00:00:00 2001
From: Tim Hunt <T.J.Hunt@open.ac.uk>
Date: Wed, 20 Mar 2024 14:13:28 +0000
Subject: [PATCH] MDL-81301 quiz: improve performance of deleting a quiz

---
 mod/quiz/lib.php            | 26 +++++++++++++-------------
 mod/quiz/tests/lib_test.php | 18 ++++++++++--------
 2 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/mod/quiz/lib.php b/mod/quiz/lib.php
index 36a613b7aa4..db6b8294e5d 100644
--- a/mod/quiz/lib.php
+++ b/mod/quiz/lib.php
@@ -2434,24 +2434,24 @@ function mod_quiz_core_calendar_get_event_action_string(string $eventtype): stri
 }
 
 /**
- * Delete question reference data.
+ * Delete all question references for a quiz.
  *
  * @param int $quizid The id of quiz.
  */
 function quiz_delete_references($quizid): void {
     global $DB;
-    $slots = $DB->get_records('quiz_slots', ['quizid' => $quizid]);
-    foreach ($slots as $slot) {
-        $params = [
-            'itemid' => $slot->id,
-            'component' => 'mod_quiz',
-            'questionarea' => 'slot'
-        ];
-        // Delete any set references.
-        $DB->delete_records('question_set_references', $params);
-        // Delete any references.
-        $DB->delete_records('question_references', $params);
-    }
+
+    $cm = get_coursemodule_from_instance('quiz', $quizid);
+    $context = context_module::instance($cm->id);
+
+    $conditions = [
+        'usingcontextid' => $context->id,
+        'component' => 'mod_quiz',
+        'questionarea' => 'slot',
+    ];
+
+    $DB->delete_records('question_references', $conditions);
+    $DB->delete_records('question_set_references', $conditions);
 }
 
 /**
diff --git a/mod/quiz/tests/lib_test.php b/mod/quiz/tests/lib_test.php
index 7a8bf421408..4b0536b4a48 100644
--- a/mod/quiz/tests/lib_test.php
+++ b/mod/quiz/tests/lib_test.php
@@ -24,6 +24,7 @@
  */
 namespace mod_quiz;
 
+use context_module;
 use core_external\external_api;
 use mod_quiz\quiz_settings;
 
@@ -106,6 +107,7 @@ class lib_test extends \advanced_testcase {
         // Setup a quiz with 1 standard and 1 random question.
         $quizgenerator = $this->getDataGenerator()->get_plugin_generator('mod_quiz');
         $quiz = $quizgenerator->create_instance(['course' => $SITE->id, 'questionsperpage' => 3, 'grade' => 100.0]);
+        $context = context_module::instance($quiz->cmid);
 
         $questiongenerator = $this->getDataGenerator()->get_plugin_generator('core_question');
         $cat = $questiongenerator->create_question_category();
@@ -121,20 +123,20 @@ class lib_test extends \advanced_testcase {
 
         // Check that the random question was deleted.
         if ($randomq) {
-            $count = $DB->count_records('question', ['id' => $randomq->id]);
-            $this->assertEquals(0, $count);
+            $this->assertEquals(0, $DB->count_records('question', ['id' => $randomq->id]));
         }
         // Check that the standard question was not deleted.
-        $count = $DB->count_records('question', ['id' => $standardq->id]);
-        $this->assertEquals(1, $count);
+        $this->assertEquals(1, $DB->count_records('question', ['id' => $standardq->id]));
 
         // Check that all the slots were removed.
-        $count = $DB->count_records('quiz_slots', ['quizid' => $quiz->id]);
-        $this->assertEquals(0, $count);
+        $this->assertEquals(0, $DB->count_records('quiz_slots', ['quizid' => $quiz->id]));
 
         // Check that the quiz was removed.
-        $count = $DB->count_records('quiz', ['id' => $quiz->id]);
-        $this->assertEquals(0, $count);
+        $this->assertEquals(0, $DB->count_records('quiz', ['id' => $quiz->id]));
+
+        // Check that any question references linked to this quiz are gone.
+        $this->assertEquals(0, $DB->count_records('question_references', ['usingcontextid' => $context->id]));
+        $this->assertEquals(0, $DB->count_records('question_set_references', ['usingcontextid' => $context->id]));
     }
 
     public function test_quiz_get_user_attempts() {