Moodle

        parent::query_start($sql, $params, $type, $extrainfo);
        $this->select_db_handle($type, $sql);
    }
 
    /**
     * This should be called immediately after each db query. It does a clean up of resources.
     *
     * @param mixed $result The db specific result obtained from running a query.
     */
    protected function query_end($result) {
        if ($this->written) {
            // Adjust the written time.
            array_walk($this->written, function (&$val) {
                if ($val === true) {
                    $val = microtime(true);
                }
            });
        }
 
        parent::query_end($result);
    }
 
    /**
     * Select appropriate db handle - readwrite or readonly.
     *
     * @param int $type Type of query.
     * @param string $sql The sql to use.
     */
    protected function select_db_handle(int $type, string $sql): void {
        if ($this->dbhreadonly && $this->can_use_readonly($type, $sql)) {
            $this->readsreplica++;
            $this->set_db_handle($this->dbhreadonly);
            return;
        }
        $this->set_dbhwrite();
    }
 
    /**
     * Check if The query qualifies for readonly connection execution.
     *

     * @return array of objects, or empty array if no records were found
     * @throws dml_exception A DML specific exception is thrown for any errors.
     */
    public function get_records_sql($sql, ?array $params=null, $limitfrom=0, $limitnum=0) {
 
        list($limitfrom, $limitnum) = $this->normalise_limit_from_num($limitfrom, $limitnum);
 
        if ($limitfrom or $limitnum) {
            if ($limitnum < 1) {
                $limitnum = "18446744073709551615";
            }
            $sql .= " LIMIT $limitfrom, $limitnum";
        }
 
        list($sql, $params, $type) = $this->fix_sql_params($sql, $params);
        $rawsql = $this->emulate_bound_params($sql, $params);
 
        $this->query_start($sql, $params, SQL_QUERY_SELECT);
        $result = $this->mysqli->query($rawsql, MYSQLI_STORE_RESULT);
        $this->query_end($result);
 
        $return = array();
 
        while($row = $result->fetch_assoc()) {
            $row = array_change_key_case($row, CASE_LOWER);
            $id  = reset($row);
            if (isset($return[$id])) {
                $colname = key($row);
                debugging("Did you remember to make the first column something unique in your call to get_records? Duplicate value '$id' found in column '$colname'.", DEBUG_DEVELOPER);
            }
            $return[$id] = (object)$row;
        }
        $result->close();
 
        return $return;
    }
 
    /**
     * Selects records and return values (first field) as an array using a SQL statement.
     *

     *     on not visible courses and 'moodle/category:viewcourselist' on all courses
     * @return array array of stdClass objects
     */
    protected static function get_course_records($whereclause, $params, $options, $checkvisibility = false) {
        global $DB;
        $ctxselect = context_helper::get_preload_record_columns_sql('ctx');
        $fields = array('c.id', 'c.category', 'c.sortorder',
                        'c.shortname', 'c.fullname', 'c.idnumber',
                        'c.startdate', 'c.enddate', 'c.visible', 'c.cacherev', 'c.deletioninprogress');
        if (!empty($options['summary'])) {
            $fields[] = 'c.summary';
            $fields[] = 'c.summaryformat';
        } else {
            $fields[] = $DB->sql_substr('c.summary', 1, 1). ' as hassummary';
        }
        $sql = "SELECT ". join(',', $fields). ", $ctxselect
                FROM {course} c
                JOIN {context} ctx ON c.id = ctx.instanceid AND ctx.contextlevel = :contextcourse
                WHERE ". $whereclause." ORDER BY c.sortorder";
        $list = $DB->get_records_sql($sql,
                array('contextcourse' => CONTEXT_COURSE) + $params);
 
        if ($checkvisibility) {
            $mycourses = enrol_get_my_courses();
            // Loop through all records and make sure we only return the courses accessible by user.
            foreach ($list as $course) {
                if (isset($list[$course->id]->hassummary)) {
                    $list[$course->id]->hassummary = strlen($list[$course->id]->hassummary) > 0;
                }
                context_helper::preload_from_record($course);
                $context = context_course::instance($course->id);
                // Check that course is accessible by user.
                if (!array_key_exists($course->id, $mycourses) && !self::can_view_course_info($course)) {
                    unset($list[$course->id]);
                }
            }
        }
 
        return $list;
    }

                }
            }
            return $courses;
        }
 
        // Retrieve list of courses in category.
        $where = 'c.id <> :siteid';
        $params = array('siteid' => SITEID);
        if ($recursive) {
            if ($this->id) {
                $context = context_coursecat::instance($this->id);
                $where .= ' AND ctx.path like :path';
                $params['path'] = $context->path. '/%';
            }
        } else {
            $where .= ' AND c.category = :categoryid';
            $params['categoryid'] = $this->id;
        }
        // Get list of courses without preloaded coursecontacts because we don't need them for every course.
        $list = $this->get_course_records($where, $params, array_diff_key($options, array('coursecontacts' => 1)), true);
 
        // Sort and cache list.
        self::sort_records($list, $sortfields);
        $coursecatcache->set($cachekey, array_keys($list));
        $coursecatcache->set($cntcachekey, count($list));
 
        // Apply offset/limit, convert to core_course_list_element and return.
        $courses = array();
        if (isset($list)) {
            if ($offset || $limit) {
                $list = array_slice($list, $offset, $limit, true);
            }
            // Preload course contacts if necessary - saves DB queries later to do it for each course separately.
            if (!empty($options['coursecontacts'])) {
                self::preload_course_contacts($list);
            }
            // Preload custom fields if necessary - saves DB queries later to do it for each course separately.
            if (!empty($options['customfields'])) {
                self::preload_custom_fields($list);
            }

    }
 
    /**
     * Returns HTML to print list of available courses for the frontpage
     *
     * @return string
     */
    public function frontpage_available_courses() {
        global $CFG;
 
        $chelper = new coursecat_helper();
        $chelper->set_show_courses(self::COURSECAT_SHOW_COURSES_EXPANDED)->
                set_courses_display_options(array(
                    'recursive' => true,
                    'limit' => $CFG->frontpagecourselimit,
                    'viewmoreurl' => new moodle_url('/course/index.php'),
                    'viewmoretext' => new lang_string('fulllistofcourses')));
 
        $chelper->set_attributes(array('class' => 'frontpage-course-list-all'));
        $courses = core_course_category::top()->get_courses($chelper->get_courses_display_options());
        $totalcount = core_course_category::top()->get_courses_count($chelper->get_courses_display_options());
        if (!$totalcount && !$this->page->user_is_editing() && has_capability('moodle/course:create', context_system::instance())) {
            // Print link to create a new course, for the 1st available category.
            return $this->add_new_course_button();
        }
        return $this->coursecat_courses($chelper, $courses, $totalcount);
    }
 
    /**
     * Returns HTML to the "add new course" button for the page
     *
     * @return string
     */
    public function add_new_course_button() {
        global $CFG;
        // Print link to create a new course, for the 1st available category.
        $output = $this->container_start('buttons');
        $url = new moodle_url('/course/edit.php', array('category' => $CFG->defaultrequestcategory, 'returnto' => 'topcat'));
        $output .= $this->single_button($url, get_string('addnewcourse'), 'get');
        $output .= $this->container_end('buttons');

                        require_once($CFG->dirroot .'/mod/forum/lib.php');
                        if (($newsforum = forum_get_course_forum($SITE->id, 'news')) &&
                                ($forumcontents = $this->frontpage_news($newsforum))) {
                            $newsforumcm = get_fast_modinfo($SITE)->instances['forum'][$newsforum->id];
                            $output .= $this->frontpage_part('skipsitenews', 'site-news-forum',
                                $newsforumcm->get_formatted_name(), $forumcontents);
                        }
                    }
                    break;
 
                case FRONTPAGEENROLLEDCOURSELIST:
                    $mycourseshtml = $this->frontpage_my_courses();
                    if (!empty($mycourseshtml)) {
                        $output .= $this->frontpage_part('skipmycourses', 'frontpage-course-list',
                            get_string('mycourses'), $mycourseshtml);
                    }
                    break;
 
                case FRONTPAGEALLCOURSELIST:
                    $availablecourseshtml = $this->frontpage_available_courses();
                    $output .= $this->frontpage_part('skipavailablecourses', 'frontpage-available-course-list',
                        get_string('availablecourses'), $availablecourseshtml);
                    break;
 
                case FRONTPAGECATEGORYNAMES:
                    $output .= $this->frontpage_part('skipcategories', 'frontpage-category-names',
                        get_string('categories'), $this->frontpage_categories_list());
                    break;
 
                case FRONTPAGECATEGORYCOMBO:
                    $output .= $this->frontpage_part('skipcourses', 'frontpage-category-combo',
                        get_string('courses'), $this->frontpage_combo_list());
                    break;
 
                case FRONTPAGECOURSESEARCH:
                    $output .= $this->box($this->course_search_form(''), 'd-flex justify-content-center');
                    break;
 
            }
            $output .= '<br />';

    $editbutton = $OUTPUT->edit_button($editurl);
    $PAGE->set_button($editbutton);
}
 
echo $OUTPUT->header();
 
// Print Section or custom info.
if (!empty($CFG->customfrontpageinclude)) {
    // Pre-fill some variables that custom front page might use.
    $modnames = get_module_types_names();
    $modnamesplural = get_module_types_names(true);
    $mods = $modinfo->get_cms();
 
    include($CFG->customfrontpageinclude);
 
} else if ($siteformatoptions['numsections'] > 0) {
    echo $courserenderer->frontpage_section1();
}
 
echo $courserenderer->frontpage();
 
if ($editing && has_capability('moodle/course:create', context_system::instance())) {
    echo $courserenderer->add_new_course_button();
}
echo $OUTPUT->footer();