Php 未定义属性：Purchase:：$Purchase\u型号codeigniter

这是我一生中见过的最奇怪的错误，因为昨天它起作用了，而我今天醒来，它不起作用了。这就是错误：

A PHP Error was encountered

Severity: Notice

Message: Undefined property: Purchase::$purchase_model

Filename: controllers/purchase.php

Line Number: 67

这是控制器代码 类购买扩展CI_控制器{

function __construct()
{
    parent::__construct();
    $this->load->model('purchase_model', 'user_model');
    $this->load->helper(array('form', 'url'));
    $this->load->library(array('form_validation', 'upload'));
}   

 function steptwo()
{   
    if($this->input->post('templateid') == NULL){
        redirect('templates');
        }
    $data =$_POST;
    if($this->session->userdata('userName')){
    $data['name']=$this->session->userdata('userName'); 
    }else{ $data['name'] = NULL;}
    $data['paymentplans'] = $this->purchase_model->GetPplan(array('id_template_type' => $_POST['idtype']));
    $this->load->view('step-two', $data);
}

A以下是我的型号代码：

   class Purchase_Model extends CI_Model
    {
        function GetPplan($options = array())
{
    // Qualification
    if(isset($options['id_template_type']))
        $this->db->where('id_template_type', $options['id_template_type']);

    // limit / offset
    if(isset($options['limit']) && isset($options['offset']))
        $this->db->limit($options['limit'], $options['offset']);
    else if(isset($options['limit']))
        $this->db->limit($options['limit']);

    // sort
    if(isset($options['sortBy']) && isset($options['sortDirection']))
        $this->db->order_by($options['sortBy'], $options['sortDirection']);


    $query = $this->db->get("template_payment_plan");

    if(isset($options['count'])) return $query->num_rows();

    if(isset($options['template_payment_planid']) || isset($options['detail']))
        return $query->row(0);

    return $query->result();
}    
 }

我已经完成了$autoload['libraries]=array（'database'，'session'）；所以我认为这不是问题所在

如果有人知道错误是什么，我将非常感激

$this->load->model('purchase_model', 'user_model');

在这里加载称为用户模型的购买模型，如果要加载两个模型，请执行以下操作：

$this->load->model('purchase_model');
$this->load->model('user_model');

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controllers/purchase.php中的哪一行是67？