如何将表单输入数据与自定义codeigniter表单验证器中的数据库数据进行比较？

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

class Custom_validator
{
    protected $CI;

    public function __construct()
    {
        $this->CI =& get_instance();
        $this->CI->load->database(); // 加载数据库类
    }

    // 自定义验证规则方法
    public function compare_data($str, $field)
    {
        list($table, $column) = explode('.', $field, 2);

        $query = $this->CI->db->select($column)
                             ->from($table)
                             ->where($column, $str)
                             ->get();

        if ($query->num_rows() === 0) {
            return FALSE; // 数据库中不存在该数据
        } else {
            return TRUE; // 数据库中存在该数据
        }
    }
}

$config = array(
    'custom_validation' => array(
        array(
            'field' => 'input_field',
            'label' => 'Input Field',
            'rules' => 'required|compare_data[table_name.column_name]'
        )
    )
);

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

class Your_controller extends CI_Controller
{
    public function __construct()
    {
        parent::__construct();
        $this->load->library('form_validation');
        $this->load->library('custom_validator'); // 加载自定义验证器类
    }

    public function your_form_submit()
    {
        $this->form_validation->set_rules($this->config->item('custom_validation'));

        if ($this->form_validation->run() === FALSE) {
            // 验证失败
        } else {
            // 验证成功
        }
    }
}