PHP mysqli query: couldn't fetch mysqli

Question

I am trying to make a db connection and check a table for existing data. However I recieve this error and I am unable to find the cause:

: mysqli::query(): Couldn't fetch mysqli in on line ：mysqli :: query（）：无法在第行的获取mysqli

: mysql_fetch_assoc() expects parameter 1 to be resource, null given in on line ：mysql_fetch_assoc（）期望参数1为资源，在第行的给出null

class dbHandler {

    static $dbObj          = null;
    protected $db_host     = 'localhost';       #db host
    protected $db_username = 'user';  #db username
    protected $db_password = 'password';        #db password
    protected $db_name     = 'db';  #db name

    function __construct()
    {
        # connect if not connected
        if(self::$dbObj === null)
        {
            self::$dbObj = new mysqli($this->db_host, $this->db_username, $this->db_password, $this->db_name)
            or die($this->dbObj->error);
        }

        mysqli_set_charset(self::$dbObj, "utf8");

    }

    // query: query the db
    public function query($query)
    {
        return self::$dbObj->query($query);
    }

}

/*
    class userLogin
    create user login
*/
class userLogin {

    private $username;
    private $password;

    function __construct($username, $password) {

        $this->_dbConn = new dbHandler();

        $this->username = $username;
        $this->password = $password;

    }

    public function verifyCredentials() {

        if($this->verifyUsername())
        {

        } else {

            exit;

        }

        if($this->verifyPassword())
        {

        } else {

            exit;

        }


    }

    private function verifyUsername() {

        if(!(preg_match('/[^a-z_\-0-9]/i', $this->username)))
        {

            return true;

        }

    }

    private function verifyPassword() {

        $query  = "SELECT * FROM tbl_user";
        $result = $this->_dbConn->query($query);
        $row    = mysql_fetch_assoc($result);

        var_dump($row);
    }

}

What am I doing wrong here?

Answer 1

All your wrapper is over a mysqli object oriented way, and suddenly you have this line?

$row    = mysql_fetch_assoc($result);

You have to use the fetch_assoc from the mysqli result object

$result->fetch_assoc()

Answer 2

Your SQL query is clearly failing. Why you have a function query to call a query I don't know but I have a feeling that is the route cause of your issue. You would be better off with something like this:

class dbHandler extends mysqli {

    protected $db_host     = 'localhost';       #db host
    protected $db_username = 'user';  #db username
    protected $db_password = 'password';        #db password
    protected $db_name     = 'db';  #db name

    function __construct()
    {
            parent::__construct($this->db_host, $this->db_username, $this->db_password, $this->db_name);
            if($this->connect_errno)
            {
                    trigger_error('Unable to connect to the database [' . $this->connect_errno . ']: ' . $this->connect_error, E_USER_ERROR);
            }

    }

    public function __destruct()
    {
        parent::close();
    }

}

/*
    class userLogin
    create user login
*/
class userLogin {

    private $username;
    private $password;

    function __construct($username, $password) {

        $this->_dbConn = new dbHandler();

        $this->username = $username;
        $this->password = $password;

    }

    public function verifyCredentials() {

        if($this->verifyUsername())
        {

        } else {

            exit;

        }

        if($this->verifyPassword())
        {

        } else {

            exit;

        }


    }

    private function verifyUsername() {

        if(!(preg_match('/[^a-z_\-0-9]/i', $this->username)))
        {

            return true;

        }

    }

    private function verifyPassword() {

        $query  = "SELECT * FROM tbl_user";
        $result = $this->_dbConn->query($query);
            if($this->_dbConn->errno)
            {
                trigger_error('Error fetching users from table. Query: ' . $query . '. Error: ' . $this->_dbConn->error);
                return false;
            }
            if($result->num_rows)
            {
                while($row = $result->fetch_assoc())
                {
                    var_dump($row);
                }
            }
    }

}

Let me know how you get on with that.

Answer 3

So... I never gave the mysql user from localhost any grants. Only from the remote LAN. Problemo solved.

Answer 4

Probably you are closing the connection too early? DBConnect->close(); ?

so, if you try to execute any query after that, you will get an error!