how to check if username already exists in codeigniter

Question

I am working on a site in codeigniter.I am not so expert using framework.Here I have to check if email already exists in database.I have coded the required functionality but

Answer 1

no need to a make a special function, this is enough

$this->form_validation->set_rules(
    'email', 'Email', 'trim|required|valid_email|is_unique'
);