Cannot access empty property php class

Question

I'm trying to learn OOP, and some of its concept. I've following class for users:

    class Users
    {

        private $host   = DB_HOST;
        private $user   = DB_USERNAME;
        private $pass   = DB_PASSWORD;
        private $dbname = DB_NAME;

        private $conn;
        private $stmt;
        public  $error;

        function __construct()
        {
            $dsn = 'mysql:host='.$this->host.';dbname='.$this->dbname.';charset=utf8';
            $options = array(
                PDO::ATTR_PERSISTENT => true,
                PDO::ATTR_ERRMODE    => PDO::ERRMODE_EXCEPTION
            );
            try {
                $this->conn = new PDO($dsn,$this->user,$this->pass,$options);
            } catch (PDOException $e) {
                $this->error = $e->getMessage();
            }
        }

        private function mysql_execute_query($sql,$params)
        {
            $this->stmt = $this->conn->prepare($sql);
            $this->stmt->execute($params);
            return $this->$stmt;
        }

        public function find_user_by_provider_uid($provider,$provider_uid)
        {
            $sql = 'SELECT * FROM users WHERE provider = :provider AND provider_uid = :provider_uid LIMIT 1';
            $params = array(
                ':provider'     => $provider,
                ':provider_uid' => $provider_uid
            );
            $result = $this->mysql_execute_query($sql,$params);
            return $result->fetch();
        }
}

First of all is there some tip that comes to mind for structuring this code better? or using more features of oop?

Second, it fails with following error:

PHP Notice: Undefined variable: stmt PHP Fatal error: Cannot access empty property

Both of this lines refer to return $this->$stmt; inside mysql_execute_query

My hunch is that it has something to do with it being private function. But I cannot tell.

Any ideas?

You used $this->stmt in one case and $this->$stmt in another. Don't you see the difference? — zerkms
– zerkms, Commented Feb 9, 2014 at 9:48
@salivan please inject a complete PDO instance in your class, instead of creating new DB connection every time you construct an instance of Users. Also, why are you using emulated prepares? — tereško
– tereško, Commented Feb 9, 2014 at 11:15
@salivan yes, that's correct. The emulation was turned on by default because pre-5.1 MySQL version did not support prepared statements. You could say it was a very short-sighed patch for a temporary problem. PHP core team has this nasty fetish for backwards compatibility =/ Also on a different note, when you pass parameters through execute() they all are bound as PDO::PARAM_STR. You might want to look int PDO's bintParam() methods, since some of your values looks kinda like integers and should be bound as such. — tereško
– tereško, Commented Feb 9, 2014 at 14:00
No, I mean in the constructor. Basically you do $user = new Users(new PDO('mysql:...', $user, $pass)); or better: $pdo = new PDO(...); $users = new Users($pdo); $docs = new Documents($pdo); .. etc. This way you can share the same connection instance between multiple object. When you pass an object as parameter, it does not get copied. — tereško
– tereško, Commented Feb 9, 2014 at 14:31

sergio · Accepted Answer · 2014-02-09 09:48:57Z

3

Here the error:

return $this->$stmt;

But should be:

return $this->stmt;

answered Feb 9, 2014 at 9:48

sergio

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1 Comment

user796443 Over a year ago

I repeat myself, I'm blind :|

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