From e226a86d7654656a2f3eff1b7ce956dfe73eb4ed Mon Sep 17 00:00:00 2001
From: Brian King <brian@liip.ch>
Date: Thu, 4 Oct 2012 18:25:41 +0200
Subject: [PATCH] MDL-36035 course: reduce database queries when calling
 print_whole_category_list

On a Moodle with 1252 course categories, this reduces the database
reads from 1313 to 62 for course/index.php
---
 course/lib.php | 49 ++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 44 insertions(+), 5 deletions(-)

diff --git a/course/lib.php b/course/lib.php
index a58b86ad3c9..36814d2dbc8 100644
--- a/course/lib.php
+++ b/course/lib.php
@@ -2179,7 +2179,7 @@ function get_course_category_tree($id = 0, $depth = 0) {
  * Recursive function to print out all the categories in a nice format
  * with or without courses included
  */
-function print_whole_category_list($category=NULL, $displaylist=NULL, $parentslist=NULL, $depth=-1, $showcourses = true) {
+function print_whole_category_list($category=NULL, $displaylist=NULL, $parentslist=NULL, $depth=-1, $showcourses = true, $categorycourses=NULL) {
     global $CFG;
 
     // maxcategorydepth == 0 meant no limit
@@ -2191,9 +2191,17 @@ function print_whole_category_list($category=NULL, $displaylist=NULL, $parentsli
         make_categories_list($displaylist, $parentslist);
     }
 
+    if (!$categorycourses) {
+        if ($category) {
+            $categorycourses = flattened_course_category_tree($category->id);
+        } else {
+            $categorycourses = flattened_course_category_tree();
+        }
+    }
+
     if ($category) {
         if ($category->visible or has_capability('moodle/category:viewhiddencategories', context_system::instance())) {
-            print_category_info($category, $depth, $showcourses);
+            print_category_info($category, $depth, $showcourses, $categorycourses[$category->id]);
         } else {
             return;  // Don't bother printing children of invisible categories
         }
@@ -2217,11 +2225,40 @@ function print_whole_category_list($category=NULL, $displaylist=NULL, $parentsli
             $down = $last ? false : true;
             $first = false;
 
-            print_whole_category_list($cat, $displaylist, $parentslist, $depth + 1, $showcourses);
+            print_whole_category_list($cat, $displaylist, $parentslist, $depth + 1, $showcourses, $categorycourses);
         }
     }
 }
 
+/**
+ * Gets an array whose keys are category ids an whose values are arrays of courses in the
+ * corresponding category.
+ *
+ * @param int $categoryid
+ * @return array
+ */
+function flattened_course_category_tree($categoryid=0) {
+    $tree = get_course_category_tree($categoryid);
+    $flattened = array();
+    foreach ($tree as $category) {
+        gather_flattened_courses($flattened, $category);
+    }
+    return $flattened;
+}
+
+/**
+ * Recursive function to help flatten the course category tree
+ *
+ * @param $flattened
+ * @param $category
+ */
+function gather_flattened_courses(&$flattened, $category) {
+    $flattened[$category->id] = $category->courses;
+    foreach ($category->categories as $childcategory) {
+        gather_flattened_courses($flattened, $childcategory);
+    }
+}
+
 /**
  * This function will return $options array for html_writer::select(), with whitespace to denote nesting.
  */
@@ -2243,7 +2280,7 @@ function make_categories_options() {
  * Prints the category info in indented fashion
  * This function is only used by print_whole_category_list() above
  */
-function print_category_info($category, $depth=0, $showcourses = false) {
+function print_category_info($category, $depth=0, $showcourses = false, $courses=NULL) {
     global $CFG, $DB, $OUTPUT;
 
     $strsummary = get_string('summary');
@@ -2264,7 +2301,9 @@ function print_category_info($category, $depth=0, $showcourses = false) {
         $catimage = "&nbsp;";
     }
 
-    $courses = get_courses($category->id, 'c.sortorder ASC', 'c.id,c.sortorder,c.visible,c.fullname,c.shortname,c.summary');
+    if (is_null($courses)) {
+        $courses = get_courses($category->id, 'c.sortorder ASC', 'c.id,c.sortorder,c.visible,c.fullname,c.shortname,c.summary');
+    }
     $context = context_coursecat::instance($category->id);
     $fullname = format_string($category->name, true, array('context' => $context));