Can I change the database for is_unique?

[eluser]CroNiX[/eluser]
You're right that it wouldn't work because the rules don't get executed until later in the code (form_validation::run()).

If you change the database right before $this->form_validation->run() and then change it back right after (and before you do things like store/retrieve anything in the db), it might work as long as nothing else in the validation rules depend on the main database.