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

$this->form_validation->set_rules('username', 'userName', 'required|callback_exists_username');


#uniqueness of username
    function exists_username($str)
    {
        $record_id = $this->input->post('record_id');
        $condition = array('user_id !='=>$record_id,'username'=>$str);
        $value =GetAllRecord('user_master',$condition,$is_single=true);
        if (count($value) == 0)
        {
            return TRUE;
        }
        else
        {
            $this->form_validation->set_message('exists_username', 'username already exists!');
            return FALSE;
        }
    }