It's the middle of the morning here, but that doesn't matter. I'm attempting to add tags to Twyne (I'd link that, but still haven't implemented hyperlinks in my Sam-flavoured Markdown). It's going fine, it's not a complicated thing to do really, but I'm bumping skulls with Doctrine ORM. I've used it before for a couple of projects, but not for a while, and I'd forgotten how frustrating it is to be poking at DQL or a query builder and trying to make it work --- when the equivalent SQL is simple and easy! I wouldn't mind if this was something complicated, but ordering by the count of a joined table shouldn't take an hour to figure out.
Oh, maybe it's not possible!
Can I sort by a function (for example ORDER BY RAND()) in DQL? No, it is not supported to sort by function in DQL. If you need this functionality you should either use a native-query or come up with another solution. As a side note: Sorting with ORDER BY RAND() is painfully slow starting with 1000 rows.