Fatal error: Call to a member function query() on a non-object in

Question

I am using pdo and I have set the connection string in a config file such as

$db = new PDO("mysql:host=localhost;dbname=mydbname", 'root', 'pass');

I have this query in a class , in a method/function

$query = $db->query("select aUsername,aPassword,aOnline,aLastlogin from tbl_admins where aUsername = '$username'");

and when I run my site I get that error. is it possible that the $db object is not global?

Answer 1

Not a great way of doing this but you should be able to get it working by adding global to your method/function:

function get_user($username) {
    global $db;
    $query = $db->query("select aUsername,aPassword,aOnline,aLastlogin from tbl_admins where aUsername = '$username'");
    ...
}

Working with globals this way you need to be very careful that you don't overwrite the variable at any point.

Answer 2

If you declared/instatiated $db in the global scope (or any scope other than the function/method), and tried to use it in a function/method, it will not work. Read this .

If your PDO object failed to instantiate or was unset before the method call, you may also recieved this error. Try var_dump(is_object($db)); and/or var_dump($db); to check.

You need to do one of the following:

---

Instantiate the PDO object within the method (probably not practical or best option):

function foo () {
  $db = new PDO( ... );
  ...
  $query = $db->query( ... );   
}

---

Instantiate the PDO object in the global scope and use the global keyword to import it into the method:

$db = new PDO( ... );

function foo () {
  global $db;
  $query = $db->query( ... );   
}

---

Instantiate the PDO object in the global scope and use the superglobal $GLOBALS array to access it.

$db = new PDO( ... );

function foo () {
  $query = $GLOBALS['db']->query( ... );   
}

---

Instantiate the PDO object in the global scope and pass it as a parameter to your method.

$db = new PDO( ... );

function foo ($db) {
  $query = $db->query( ... );   
}

foo($db);

---

Instantiate the PDO object in the global scope and pass into your object as a property.

$db = new PDO( ... );

class foo {

  public $db;

  public function bar ($db) {
    $query = $this->db->query( ... );   
  }

}

$foo = new foo;
$foo->db = $db;
$foo->bar($db);

Answer 3

I recommend to use a good pattern called Registry . And a simple implementation in PHP:

abstract class Registry {

    private static $_tools = array();

    public static function set($name, $value) {
        self::$_tools[$name] = $value;
    }

    public static function get($name) {
        return (isset(self::$_tools[$name]) ? self::$_tools[$name] : null);
    }

}

Usage:

$db = new PDO("mysql:host=localhost;dbname=mydbname", 'root', 'pass');
Registry::set('db', $db);

//In some other part of code
$query = Registry::get('db')->query("select aUsername,aPassword,aOnline,aLastlogin from tbl_admins where aUsername = '$username'");