未捕获的TypeError：无法读取codeigniter中未定义的属性“ length”

如何解决未捕获的TypeError：无法读取codeigniter中未定义的属性“ length”

晚上好，我尝试在codeigniter中编写库存系统代码。我想在数据表卡中显示数据。每当我运行该程序时，它都会说“ Uncaught TypeError：无法读取未定义的属性'length'”这是代码。

控制器

class Inventory extends CI_Controller{
    
    public function __construct(){
        
        parent::__construct();
        $this->load->model('inventory_model');

    }

    public function index(){
        $this->load->helper('url');
        $this->load->view('inventory');
    }

        public function fetch(){
        if ($this->input->is_ajax_request()) {
            if ($posts = $this->inventory_model->get_entries()) {
                $data = array('response' => 'success','posts' => $posts);
            }else{
                $data = array('response' => 'error','message' => 'Failed to fetch data');
            }
            echo json_encode($data);
        }else{
            echo "No direct";
        }
    }

}


?>

型号

<?php

/**
 * 
 */
class Inventory_model extends CI_Model{

    public function get_entries()
        {
                $query = $this->db->get('inventory');
                if (count($query->result())>0) {
                    return $query->result();
                }
        }
    
    
}


?>

脚本

function fetch(){

       var table = $('#example').DataTable({
         dom: 
                    "<'row'<'col-sm-12 col-md-6'l><'col-sm-12 col-md-6'<'float-md-right ml-2'B>f>>" +
                    "<'row'<'col-sm-12'tr>>" +
                    "<'row'<'col-sm-12 col-md-5'i><'col-sm-12 col-md-7'p>>",buttons: [
                'csv',{
            'text': '<i class="fa fa-id-badge fa-fw" aria-hidden="true"></i>','action': function (e,dt,node) {

               $(dt.table().node()).toggleClass('cards');
               $('.fa',node).toggleClass(['fa-table','fa-id-badge']);

               dt.draw('page');
            },'className': 'btn-sm','attr': {
               'title': 'Change views',}
               }],select: 'single','ajax': {
            'url':'<?=site_url()?>inventory/fetch','type': "post",'dataType': "json",},'columns': [
          {
            'orderable': false,'data': null,'className': 'text-center','render': function(data,type,full,meta){
                  if (type === 'display'){
                     data = '<i class="fa fa-user fa-fw"></i>';
                     data = '<img src="https://i.ibb.co/wYwKxdr/vaccine.png" alt="vaccine" border="0" class="avatar border rounded-circle">';
                  }
                  
                  return data;
               }
          },{ "data": 'vaccine_name' },{ "data": 'stock' },{ "data": 'number_of_shots' },{ "data": 'shot_taken' }
         ],'drawCallback': function (settings) {
            var api = this.api();
            var $table = $(api.table().node());
            
            if ($table.hasClass('cards')) {

               // Create an array of labels containing all table headers
               var labels = [];
               $('thead th',$table).each(function () {
                  labels.push($(this).text());
               });

               // Add data-label attribute to each cell
               $('tbody tr',$table).each(function () {
                  $(this).find('td').each(function (column) {
                     $(this).attr('data-label',labels[column]);
                  });
               });

               var max = 0;
               $('tbody tr',$table).each(function () {
                  max = Math.max($(this).height(),max);
               }).height(max);

            } else {
               // Remove data-label attribute from each cell
               $('tbody td',$table).each(function () {
                  $(this).removeAttr('data-label');
               });

               $('tbody tr',$table).each(function () {
                  $(this).height('auto');
               });
            }
         }
       })
       .on('select',function (e,indexes) {
         var rowData = table.rows(indexes).data().toArray()
         $('#row-data').html(JSON.stringify(rowData));
      })
      .on('deselect',function () {
         $('#row-data').empty();
      })
    };

    fetch();