From fd32dbfa1de464b3d08f6dbf55428085938627f3 Mon Sep 17 00:00:00 2001
From: Tim Hunt <T.J.Hunt@open.ac.uk>
Date: Thu, 3 May 2012 22:33:36 +0100
Subject: [PATCH] MDL-32633 quiz editing: recreate grade item when max changed
 from 0

---
 mod/quiz/locallib.php | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/mod/quiz/locallib.php b/mod/quiz/locallib.php
index 03fabcd7fd2..a5306ad14c5 100644
--- a/mod/quiz/locallib.php
+++ b/mod/quiz/locallib.php
@@ -461,28 +461,33 @@ function quiz_set_grade($newgrade, $quiz) {
         return true;
     }
 
+    $oldgrade = $quiz->grade;
+    $quiz->grade = $newgrade;
+
     // Use a transaction, so that on those databases that support it, this is safer.
     $transaction = $DB->start_delegated_transaction();
 
     // Update the quiz table.
     $DB->set_field('quiz', 'grade', $newgrade, array('id' => $quiz->instance));
 
-    // Rescaling the other data is only possible if the old grade was non-zero.
-    if ($quiz->grade > 1e-7) {
-        global $CFG;
+    if ($oldgrade < 1) {
+        // If the old grade was zero, we cannot rescale, we have to recompute.
+        // We also recompute if the old grade was too small to avoid underflow problems.
+        quiz_update_all_final_grades($quiz);
 
-        $factor = $newgrade/$quiz->grade;
-        $quiz->grade = $newgrade;
-
-        // Update the quiz_grades table.
+    } else {
+        // We can rescale the grades efficiently.
         $timemodified = time();
         $DB->execute("
                 UPDATE {quiz_grades}
                 SET grade = ? * grade, timemodified = ?
                 WHERE quiz = ?
-        ", array($factor, $timemodified, $quiz->id));
+        ", array($newgrade/$oldgrade, $timemodified, $quiz->id));
+    }
 
+    if ($oldgrade > 1e-7) {
         // Update the quiz_feedback table.
+        $factor = $newgrade/$oldgrade;
         $DB->execute("
                 UPDATE {quiz_feedback}
                 SET mingrade = ? * mingrade, maxgrade = ? * maxgrade
@@ -490,7 +495,7 @@ function quiz_set_grade($newgrade, $quiz) {
         ", array($factor, $factor, $quiz->id));
     }
 
-    // update grade item and send all grades to gradebook
+    // Update grade item and send all grades to gradebook.
     quiz_grade_item_update($quiz);
     quiz_update_grades($quiz);