请告诉我codeigniter有问题。当我尝试在这里登录时，结果是：
严重性：错误-->异常：在boolean/home/euroyals/bdhospitals.com/amar-pharmary/application/models/reports.php 276上调用成员函数numđrows（）
在相对文件的代码下面：

public function out_of_stock_count(){

  $this->db->select("b.manufacturer_name,a.product_name,a.generic_name,a.strength,((select ifnull(sum(quantity),0) from product_purchase_details where product_id= `a`.`product_id`)-(select ifnull(sum(quantity),0) from invoice_details where product_id= `a`.`product_id`)) as 'stock'");
       $this->db->from('product_information a');
       $this->db->join('manufacturer_information b','b.manufacturer_id=a.manufacturer_id','left');
         $this->db->having('stock < 10');
         $this->db->group_by('a.product_id');
         return $records = $this->db->get()->num_rows();