Validate form with default values?

[eluser]Sven Delle[/eluser]
Is it possible to have both a required and a callback at the same time somehow?

If I use a callback to check for existing username I cannot send any errors to the validator if the field is empty. I doesn't validate, but I'd like to send it the required error.

Any solution for that?

Well, yes:

Code:

$this->form_validation->set_rules('username', 'Username', 'required|callback_check_default_username');