I don't think this can or should be added in 1.9.x. Come to that, I don't think it should be added to 2.0 either - it would be a gigantomammoth task, and I don't think Moodle 2 needs yet more encouragement to slip to 2011.

(To answer the original post - no don't delete them, yes if you do that it will break or output odd blank parts or otherwise get confused when you look at a page that refers to the user in some way, e.g. a forum post they made.)


So back to the 'problem'.. why do you actually care if there are a handful of extra users in the user table? Data-storage-wise, a few user entries - say 21,000 - is hardly significant in the overall scheme of things. What's that, a few tens of megabytes?

It isn't possible to coherently delete users without also deleting all references to that user ever. (For example, if they made a forum post, you'd better delete it. Do you really want this to happen?) I suppose a more sensible option might be to alter all references to this user so that they point to a special 'deleted user'. But do you really want all historical data about these users, and what they did, to be splurged into one such unidentifiable überuser?

In order to implement either feature (deleting everything that references the user, or changing everything to point to the 'deleted user' user) there would need to be a new API function which would have to be implemented by every module and plugin (including third-party). That's the fundamental reason why this can't happen in 1.9.

--sam

Agree with Sam completely.

But if you really wanted to delete the user - we do fire a user_deleted event on user deletion.

If you wished to develop an unsupported module which completely deletes the user you could hook onto this event and delete the user completely in a relatively clean (but dangerous!) way.

see the hook in the code:
events_trigger('user_deleted', $user);

And docs: Development:Events (not looked to see if that documentation is complete, sorry).

ps. this is a useful hook more module authors should think about (I recall it because in cvs://contrib/patches/cleo_mis_tool I have something akin to the role_assignments table and currently patch in deletion of these references to the user deletion function in moodlelib.php from the 1.8 days. I intend to replace with a user_deleted event hook when I get round to it!)

So, wait, you actually do want to keep the mdl_user entry, but delete everything else (except log)? That's kind of the opposite of the original suggestion But it is definitely more feasible.

Even so, I'm a bit surprised that anyone would really want to suddenly delete (for instance) every forum post, glossary entry, etc made (or edited or otherwise touched) by a particular user.

This is definitely more feasible than altering the mdl_user entries, but again, is not likely to happen in 1.9 (the API might already exist thanks to the mentioned event that I didn't know about before, but it still needs to be implemented in every module, and I don't really see that happening).

Also note that if you don't keep courses forever, you don't run into this problem anyway. In other words if you have fast student turnover, you should probably arrange that you have a reasonable course turnover too; every year you could start from a new version of the course(s). [Create new versions using backup and restore without user data.] Deleting an old course will delete all the data associated with activities on that course, regardless of user status.

(Incidentally, cascade deletion is IMO an insanely dangerous tool that should virtually never be used as standard practice. And it wouldn't help in this case given that under your plan we would still need to keep the mdl_user row anyhow.)

--sam