<?php

class Datamanager {
    public $hostName = 'localhost';
    public $dbName = 'stackoverflow';
    public $dbUser = 'xxx';
    public $dbPassword = 'xxx';

    public function __construct() {
        try {
            $this->dbh = new PDO("mysql:host=$this->hostName;dbname=$this->dbName", $this->dbUser, $this->dbPassword);
        } catch(PDOException $e) {
            echo $e->getMessage();
        }
    }
    public function runQuery($query, $obj){
        try {
            $STH = $this->dbh->prepare($query);
                        $STH->bindParam(':id', $obj->user_id);

            $STH->setFetchMode(PDO::FETCH_INTO, $obj);
                        $STH->execute();
                        $STH->fetch();
        } catch(PDOException $e) {
            echo $e->getMessage();
        }
        return $obj;
    }
}

class User {
    public $user_id;
    public $user_name;
    public $user_password;
    public $session_id;
    private $dbc;

    public function __construct() {
        $this->dbc = new Datamanager();
    }

    function selectUser ($userID, $obj) {
                $this->user_id = $userID;
        $query = 'SELECT user_id, user_name, user_password, session_id FROM users WHERE user_id=:id';
        $results = $this->dbc->runQuery($query, $this);
    }
}

$userID = "1";
$test = new User;

$test->selectUser($userID, $test);

var_dump($test);