在codeigniter中的条件中的未知列

Question

我的控制器是

public function login_process()
    {
        $this->load->library('session');
        $data=array(
                    'username'=>$this->input->post('userName'),
                    'password'=>md5($this->input->post('userPwd'))
                    );
        $result = $this->Admin->login($data);

        if ($result == TRUE)
        {
            $session_data = array(
            'userId' => $result[0]->user_id,
            'username' => $result[0]->user_name,);
            $this->session->set_userdata('logged_in', $session_data);
            $this->load->view('header');
        }

        else 
        {
            $data['msg'] = array(
            'error_message' => 'Invalid Username or Password'
            );
            $this->load->view('index',$data);
        }
    }

我的模特是

class Admin extends CI_model
{
    // Read data using username and password
    public function login($data)
    {
        $this->db->select('*');
        $this->db->from('users');
        $this -> db -> where('user_name', $data['username']);
        $this -> db -> where('user_password ',$data['password']);
        $this->db->limit(1);
        var_dump($this->db);
        $query = $this->db->get();
        if ($query->num_rows() == 1) 
        {
            return true;
        } 
        else
        {
            return false;
        }
    }
}

我收到以下错误

Error Number: 1054

'where子句'中的未知列'user_name'

SELECT * FROM（users）WHERE user_name ='ddddd'和user_password ='xxx'LIMIT 1

文件名：C：\ xampp \ htdocs \ pranasInventory \ system \ database \ DB_driver.php

行号：330

请帮帮我