From 1eecb821ac41d0ca5c8173ae4c64d091107fe071 Mon Sep 17 00:00:00 2001
From: Mark Johnson <mark.johnson@catalyst-eu.net>
Date: Thu, 21 Aug 2025 13:46:56 +0100
Subject: [PATCH] MDL-86397 calendar: Filter user courses

In the calendar API, `raw_event_retrieval_strategy` accepts a list of
courses to return events for. If one or more users are also specified,
it will find the courses the are enrolled in, then call
`calendar_set_filters()` to return a sorted list of those courses, and
any groups within those courses that they can see events for. The list
of courses in then filtered to those passed to
`raw_event_retrieval_strategy`.

If the user is enrolled on lots of courses, but is only viewing the
caledar for one course, this results in a lot of redundant work to fetch
group data for their courses which is then not used. This either
involves a lot of extra complex queries, or results in an unncessary
cache hit for each course.

This change re-orders the code so that the list of enrolled courses is
filtered to just those courses being viewed, before it is passed to
`calendar_set_filters()`. This means we are only fetching group data for
those courses we will be showing events for.
---
 .../raw_event_retrieval_strategy.php          | 25 +++++++++++++------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/public/calendar/classes/local/event/strategies/raw_event_retrieval_strategy.php b/public/calendar/classes/local/event/strategies/raw_event_retrieval_strategy.php
index 3c3ad7cf54b..0ad1c4b8200 100644
--- a/public/calendar/classes/local/event/strategies/raw_event_retrieval_strategy.php
+++ b/public/calendar/classes/local/event/strategies/raw_event_retrieval_strategy.php
@@ -187,6 +187,16 @@ class raw_event_retrieval_strategy implements raw_event_retrieval_strategy_inter
         $subqueryparams = [];
         $allusercourses = [];
 
+        $groupcourses = [];
+        if (is_array($groups) && !empty($groups)) {
+            $groupcourses = $DB->get_fieldset_sql(
+                "SELECT DISTINCT courseid
+                   FROM {groups}
+                  WHERE id $insqlgroups",
+                $inparamsgroups,
+            );
+        }
+
         if (is_array($users) && !empty($users)) {
             $userrecords = $DB->get_records_sql("SELECT * FROM {user} WHERE id $insqlusers", $inparamsusers);
             foreach ($userrecords as $userrecord) {
@@ -194,13 +204,14 @@ class raw_event_retrieval_strategy implements raw_event_retrieval_strategy_inter
                 $usercourses = calendar_get_default_courses(null, 'id, category, groupmode, groupmodeforce',
                         false, $userrecord->id);
 
-                // Set calendar filters.
-                list($usercourses, $usergroups, $user) = calendar_set_filters($usercourses, true, $userrecord);
+                $filteredcourses = array_merge(
+                    is_array($courses) ? $courses : [$courses],
+                    $groupcourses, // Include courses for any groups we've specified.
+                );
+                $filteredcourses = array_filter($usercourses, fn($course) => in_array($course->id, $filteredcourses));
 
-                $filteredcourses = is_array($courses) ? $courses : [$courses];
-                $filteredcourses = array_filter($usercourses, function($course) use ($filteredcourses) {
-                    return in_array($course, $filteredcourses);
-                });
+                // Set calendar filters.
+                [$filteredcourses, $usergroups, $user] = calendar_set_filters($filteredcourses, true, $userrecord);
 
                 $allusercourses = array_merge($allusercourses, $filteredcourses);
 
@@ -215,7 +226,7 @@ class raw_event_retrieval_strategy implements raw_event_retrieval_strategy_inter
                     $subqueryconditions[] = $condition;
                     $subqueryparams = array_merge($subqueryparams, $inuserparams);
 
-                    foreach ($usercourses as $courseid) {
+                    foreach ($filteredcourses as $courseid) {
                         if (has_capability('moodle/site:accessallgroups', \context_course::instance($courseid), $userrecord)) {
                             $usergroupmembership = groups_get_all_groups($courseid, $user, 0, 'g.id');
                             if (count($usergroupmembership) == 0) {