Codeigniter is_unique for multiple fields

MY_Form_validation.php

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class MY_Form_validation extends CI_Form_validation {

  protected $CI;

	public function __construct($rules = array())
    {
        parent::__construct($rules);
        $this->CI =& get_instance();
    }


/**
 * is_unique_multiple
 * check multiple unique field at time
 * handy when checking if two or more column of some set of value
 * e.g if firstname="something" and username="something"
 * usage: 
 	is_unique_multiple[
	 	table_name,
	 	column_name1.column_name2.column_name3,
	 	post_filed_name1.post_field_name2.post_field_name3
 	]

 	*real example
 	$this->form_validation->set_rules('fee_name', 'fee_name', "required|is_unique_multiple[arasoft_fee, fee_name.fee_term.fee_users, fee_name.term.fee_users ]");
 **/
    public function is_unique_multiple($str,$data)
    {
    	$data = explode(",", $data);
    	if(count($data)<2)
    		return TRUE;

    	$table = @$data[0];
    	$str = @$data[1];
    	$str = explode(".", $str);
    	$field = @$data[2];
    	//var_dump($table,$str,$field);exit();
    	$field = empty($field) ? $str : explode(".", $field);
    	if(count($str) != count($field)){
    		return TRUE;
    	}
    	$where = [];

    	foreach ($str as $key => $value) {
    		# code...
    		$q = $this->CI->input->post($field[$key]);
    		$where[$value] = $q;
    	}
        
        $check = $this->CI->db->get_where($table, $where, 1);

        if ($check->num_rows() > 0) {

            $this->set_message('is_unique_multiple', 'This data exist already');

            return FALSE;
        }

        return TRUE;
    }
}