试图获取非对象错误的属性

Question

I need to get the number of rows returned of a certain query but it kept me this error

Trying to get property of non-object in C:\\xampp\\htdocs\\sample\\includes\\CheckUsername.php on line 18

Here's my code:

 <?php
        class Db_CheckUsername{
            protected $_conn;
            protected $_username;
            protected $_errors = array();

            public function __construct($username,$conn){
                $this->_username = $username;
                $this->_conn = $conn;
            }

            public function isUsernameAvailable(){
                $sql = "SELECT ";
                $sql .= "FROM accounts ";
                $sql .= "WHERE username = {$this->_username}";

                $result = $this->_conn->query($sql);
                $numRows = $result->num_rows;

                if($numRows == 0){
                    return true;
                }else{
                    return false;
                }
            }
        }
    ?>

How do I resolve this?

Answer 1

SELECT FROM accounts

is probably invalid. You probably want SELECT * FROM or SELECT 1 FROM .

Answer 2

I won't give you the solution because I think you need to develop some basic troubleshooting skills.

• Inspect your data. What data does $result contain? Check with var_dump .
• Is your query correct? Print the query to see it. Copy and paste the exact query into an SQL prompt to see if it's working.

Answer 3

You aren't checking for errors in your query. If an error occured, $result will be false, which is exactly the case. You have a syntax error in your query.