Codeigniter，数据库错误，严重性:4096消息:类CI_DB_mysql_result的对象不能转换为字符串 - Codeigniter, Database Errror, Severity: 4096 Message: Object of class CI_DB_mysql_result could not be converted to string

Codeigniter, Database Errror, Severity: 4096 Message: Object of class CI_DB_mysql_result could not be converted to string

我试图从名为"post_id的数据库中获得一个属性值，以便在其他地方使用。

这是我的模型代码。

$copy_query = "SELECT post_id FROM posts order by post_id DESC limit 1"; //query for selecting last post's post_id
$result = $this->db->query($copy_query);    //adding that post_id to the $result variable 
$sub_data = array(
                    'study_education_level' => $this->input->post('sub_education_level'),
                    'tourism_country' => $this->input->post('sub_tourism_country'),
                    'tourism_place_name' => $this->input->post('sub_tourism_placeName'),
                    'post_id' => $result
            );
            $this->db->insert('subcategories',$sub_data);

但是当我运行代码时，它会给我两个ERROR

遇到PHP错误

Severity: 4096
Message: Object of class CI_DB_mysql_result could not be converted to string
Filename: mysql/mysql_driver.php
Line Number: 553

和2.

A Database Error Occurred
Error Number: 1064
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 1
INSERT INTO `subcategories` (`study_education_level`, `tourism_country`, `tourism_place_name`, `post_id`) VALUES ('Higher Study', '', '', )
Filename: C:'xampp'htdocs'learn'system'database'DB_driver.php
Line Number: 331

提前感谢!

顺便说一下，我已经解决了这个问题。

$result = $this->db->query($copy_query);    //adding that post_id to the variable   
            if ($result->num_rows() > 0)
            {
                    foreach ($result->result() as $row)
                    {
                            $post_id_plz =  $row->post_id;
                    }
            }