General developer forum

We've had an interesting patch (against 1.5) sleeping on our hard drive for a while, that you may want to play with ;)

From a user's perspective, the patch adds an option in the course creation page, "Is this a metacourse? (yes/no) checkbox". If you mark it as a metacourse, the student enrolment page changes. Instead of listing (or offering to search for) students, it lists/searches for courses.

For every course you 'enrol' to the metacourse, all the students in that course are enrolled in the metacourse. Once the metacourse is configured, it works transparently: every time a student enro;ls to (or unenrolls from) a course, she is magically enrolled/unenrolled from the relevant metacourse(s) (although it doesn't happen immediately, may take an hour to show up).

The code prevents nesting of metacourses, to avoid infinite loops.

From the underlying code perspective, we didn't change the enrolment mechanisms -- no extra joins or SQL magic. We added one column to mdl_course to hold the boolean flag of whether it is a metacourse, and we added a table holding the 'course enrolments' that make a metacourse enrolment (it describes a many-to-many relationship between courses). 

We have a modified student enrolment page that lists courses, and every time a course is added/removed, it will add/remove the student enrolments to the mdl_user_student table (so the enrolments appear to be "normal" enrolments to the rest of the Moodle code).

After the metacourse is setup, the student enrolments are maintained by moodle's cron.php. We could add logic to enrol_student() and unenrol_student() to make the logic in cron superfluous and the whole thing more scalable and elegant.

We've had this code in production on a large Moodle install where the 'normal' enrolments are coming from an LDAP repository (we are using the LDAP enrolment plugin) and Moodle admins define courses where all the students of (for instance) computer science courses are enrolled. All they do is select the CompSci courses in the metacourse, and it's done; when new enrolments come through the LDAP plugin, they are automatically enrolled in the relevant metacourse.

The code does need a bit of testing in other installs, to make sure we didn't overlook anything, so it'd be great if you can give it a test, and let us know what you think.

Today's patch is brough to you by the letters "NZVLE", in collaboration with Penny Leach, who did the thinking and programming. As usualy, it's experimental, so if it breaks you get to keep all the parts.

The patch applies cleanly to today's CVS HEAD; to apply, unzip the attached file, patch Moodle with meta.diff, place the import_students.php and import_students.html in course and hack your database thus:

- modify your {prefix_}course table saying
  (mysql) ALTER TABLE {prefix_}course ADD COLUUMN meta_course INT(1) UNSIGNED NOT NULL DEFAULT '0'
  (postgres) ALTER TABLE {prefix_}course ADD COLUUMN meta_course INTEGER NOT NULL DEFAULT '0'

- add the extra table & indexes
(mysql)
CREATE TABLE `{prefix_}meta_course` (
        `id` int(1) unsigned NOT NULL auto_increment,
        `parent_course` int(10) NOT NULL default 0,
        `child_course` int(10) NOT NULL default 0,
        PRIMARY KEY (`id`),
        KEY `parent_course` (parent_course),
        KEY `child_course` (child_course)
); 

(postgres)
CREATE TABLE {prefix_}meta_course (
        id SERIAL primary key,
        parent_course integer NOT NULL,
        child_course integer NOT NULL
);
CREATE INDEX {prefix_}meta_course_parent_idx ON prefix_meta_course
(parent_course);
CREATE INDEX {prefix_}meta_course_child_idx ON prefix_meta_course
(child_course);


And finally, in cron.php find the line that updates enrolments:
  $enrol->cron();
and add a call to sync_metacourses() right after that.