在简单的php页面中无法多次使用自定义PDO类

Question

I coded a custom Database.class.php class that encapsulates a PDO object to interact with a MySQL database.

<?php

require_once('./classes/configs/Config.php');
class Database
{
    private static $instance = null; 

    private  function __construct()
    {}

    public static function getInstance()
    {
        if (self::$instance == null)
        {
            self::$instance = new PDO(
                "mysql:host=".Config::DB_HOST.";dbname=".Config::DB_NAME."", 
                Config::DB_USER, 
                Config::DB_PWD);

            return self::$instance; 
        }
    }
}
?>

I've also coded a custom UserDAO.class.php which allows me for an easier way of performing CRUD operations. For example, when I want to find a user in my database, I procede like so: $userdao->find('tim') and store my findings in a custom user.class.php object. (This class obviously calls a static Database.class.php object to use the PDO object in that class). Here is the find function in my UserDAO.class.php

public static function find($username)
    {
        $db = Database::getInstance();

        $pstmt = $db->prepare("SELECT * FROM users WHERE username = :x");
        $pstmt->execute(array(':x' => $username));

        $result = $pstmt->fetch(PDO::FETCH_OBJ);
        $p = new User();

        if ($result)
        {

            $p->setUser_id($result->user_id);
            $p->setUsername($result->username);
                        $p->setFirst_name($result->first_name);
                        $p->setLast_name($result->last_name);
                        $p->setEmail($result->email);
            $p->setRegistration_date($result->registration_date);
            $pstmt->closeCursor();
            return $p;
        }
        $pstmt->closeCursor();
        return null;
    }

The problem is that I seem to be unable to use the $userdao object more than once on a simple php page.

$userdao = new UserDAO();
$user5=$userdao->find('tim');
echo"<h3>".$user5."</h3>";  // this works fine (I have a toString function)
$user6=$userdao->find("john"); // this does not work....rest of the page is blank!!!!
echo"<h3>".$user6."</h3>";  

Answer 1

You have error here - you return self::$instance only if self::$instance == null

public static function getInstance() {
    if (self::$instance == null)
    {
        self::$instance = new PDO(
            "mysql:host=".Config::DB_HOST.";dbname=".Config::DB_NAME."", 
            Config::DB_USER, 
            Config::DB_PWD);
        // return self::$instance; // moved down

    }
    return self::$instance; // this is the fix
}

also you could eaisly debug it by yourself the reason why rest of the page is blank!!!!" is because you have disabled error reporting. change php.ini or use error_reporting() to show PHP errors and warnings

See:

• http://php.net/manual/en/errorfunc.configuration.php (display_errors, error_reporting)
• http://php.net/manual/en/function.error-reporting.php

the reason why page is blank is because PHP is throwing fatal error (you are trying to use method find on null), but since you have no error reporting nothing shows up

there is no way to develop applications without error reporting, you must always have it enabled in development environment