破译“记住我”上的堆栈跟踪错误 Function

Question

I have received my first stack trace error on a PHP beginners CRUD educational project. Since I am a newbie, I am having trouble with it. After many hours of research I believe I may have narrowed down the error to my logout method, (although this is merely my opinion). If someone can help me correct my error I would greatly appreciate it. I will attach some of my code here. Since I am not exactly sure where the error lies, I may have left something out. If that is the case I am more than happy to supply more code. Thank you in advance.

My error occurs when I click the logout button;

Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error in C:\xampp\htdocs\test_site.com\classes\db.php:51 Stack trace: #0 C:\xampp\htdocs\test_site.com\classes\db.php(51): PDOStatement->fetchAll(5) #1 C:\xampp\htdocs\test_site.com\classes\db.php(77): DB->query('DELETE FROM use...', Array) #2 C:\xampp\htdocs\test_site.com\classes\db.php(90): DB->action('DELETE', 'users_session', Array) #3 C:\xampp\htdocs\test_site.com\classes\user.php(243): DB->delete('users_session', Array) #4 C:\xampp\htdocs\test_site.com\logout.php(5): User->logout() #5 {main} thrown in C:\xampp\htdocs\test_site.com\classes\db.php on line 51

If I comment out this code;

 $this->_db->delete('users_session', array('user_id', '=', $this->data()->id)); 

I do not get the fatal error. However, I am unable to delete the entry that was made in the database to retain the hash for the 'remember me' cookie.

According to the stack trace error and everything that I have tried, I keep getting this line as some sort of problem.

 $this->_results = $this->_query->fetchAll(PDO::FETCH_OBJ);

I do not know why I am having an issue here. I know this error seems huge and unmanageable but I am hoping someone here has an eye for these stack trace problems and can help me with this issue. Thanks again.

enter code here
 /////////////////////////////////////////////////////////// 


  <?php     
     require_once 'corefiles/initiation.php';       

     if(Input::exists()) {
    if(Token::check(Input::get('token'))) {
        
        $validate = new Validate();
        $validation = $validate->check($_POST, array(
            'username' => array('required' => true),
            'password' => array('required' => true)
        ));
        
        if($validation->passed()) {
            $user = new User();
            
            $remember = (Input::get('remember') === 'on') ? true : false;                
            $login = $user->login(Input::get('username'), Input::get('password'), $remember);
            
            if($login) {
                Redirect::redirectto('index.php');                                  
            } else {
                echo '<p>Sorry, logging in failed.</p>';
            }
            
        } else {
            foreach($validation->errors() as $error) {
                echo $error, '<br>';
            }
        }           
    }
}


 <form action="" method="post">
   <div class="field">
       <label for="username">Username</label>
       <input type="text" name="username" id="username" autocomplete="off">
   </div>

   <div class="field">
       <label for="password">Password</label>
        <input type="password" name="password" id="password">   
   </div>   

   <div class="field">
      <label for="remember">
        <input type="checkbox" name="remember" id="remember"> Remember me
      </label>
    </div>

    <input type="hidden" name="token" value="<?php echo Token::generate(); ?>">
    <input type="submit" value="Log in">
 </form>

 ////////////////////////////////////////////////////////////
class User {
    private $_db,
            $_data,
            $_sessionName,
            $_cookieName,
            $_isLoggedIn;               
    
    public function __construct($user = null) {
        $this->_db = DB::getInstance();             
        
        $this->_sessionName = Config::get('session/session_name');
        $this->_cookieName = Config::get('remember/cookie_name');
        
        if(!$user) {
            if(Session::exists($this->_sessionName)) {
                $user = Session::get($this->_sessionName);
                
                if($this->find($user)) {
                    $this->_isLoggedIn = true;
                } 
            }
        } else {
            $this->find($user);
        }
    }

     public function logout() { 
        // THIS LINE IS WHAT I BELIEVE IS THE PROBLEM. IF COMMENTED OUT I CAN LOGOUT HOWEVER
        // THE HASH IN THE DATABASE DOES NOT GET DELETED.               
        $this->_db->delete('users_session', array('user_id', '=', $this->data()->id));            
        Session::delete($this->_sessionName);
        Cookie::delete($this->_cookieName);           
    }

/////////////////////////////////////////////////////////////    
class DB {
    private static $_instance = null;
    private $_pdo = null,
            $_query = null,
            $_error = false,
            $_results = null,
            $_count = 0;
    
    public $debug = true;
    
    private function __construct() {
        try {
            $this->_pdo = new PDO('mysql:host=' . Config::get('mysql/host') . ';dbname=' . 
            Config::get('mysql/db'), Config::get('mysql/username'), Config::get('mysql/password'));
            
            if($this->debug) {
                $this->_pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            }
                            
        } catch(PDOException $e) {
            die($this->debug ? $e->getMessage() : '');
        }           
    }
    public function query($sql, $params = array()) {
        $this->_error = false;
        if($this->_query = $this->_pdo->prepare($sql)) {                
            $x = 1;
            if(count($params)) {
                foreach($params as $param) {
                    $this->_query->bindValue($x, $param);
                    $x++;                       
                }                   
            }               
            
            if($this->_query->execute()){
                // THIS "FETCH" CODE MAY BE AN ISSUE AS WELL. 
                //$this->_results = $this->_query->fetchObject();
                $this->_results = $this->_query->fetchAll(PDO::FETCH_OBJ);//THIS IS db.php line 51
                
                
                $this->_count = $this->_query->rowCount();    
                
            } else {
                $this->_error = true;
            }
        }
        
        return $this;
    }
     public function action($action, $table, $where = array()) {
        if(count($where) === 3) {
            $operators = array('=', '>', '<', '>=', '<=');
            
            $field      = $where[0];
            $operator   = $where[1];
            $value      = $where[2];
            
            if(in_array($operator, $operators)) {
                $sql = "{$action} FROM {$table} WHERE {$field} {$operator} ?";
                
                if(!$this->query($sql, array($value))->error()) {
                    return $this;
                }
            }
        }
        return false;
    }
    
    public function get($table, $where) {
        return $this->action('SELECT *', $table, $where);
    }
    
    public function delete($table, $where) {
        return $this->action('DELETE', $table, $where);
    }


    /////////////////////////////////////////////////////
    //Logout script
        require_once 'core/init.php';       

        $user = new User();
        $user->logout();
         //var_dump( $user->logout() );

         //redirect script
        Redirect::redirectto('index.php');   

Answer 1

You're doing a fetchAll after a delete query.

Try checking how many results are returned before calling fetchAll in the DB query method and see if that fixes the issue.

public function query($sql, $params = array()) {
    $this->_error = false;
    if($this->_query = $this->_pdo->prepare($sql)) {                
        $x = 1;
        if(count($params)) {
            foreach($params as $param) {
                $this->_query->bindValue($x, $param);
                $x++;                       
            }                   
        }               
        
        if($this->_query->execute()){
            if(substr($sql, 0, 6) === "SELECT"){
                $this->_results = $this->_query->fetchAll(PDO::FETCH_OBJ);
            } else {
                 $this->_results = null;
            }  
            $this->_count = $this->_query->rowCount();
        } else {
            $this->_error = true;
        }
    }
    
    return $this;
}

Answer 2

your " Fatal Error " is an " Uncaught PDOException ". What this is is that your PDO code should be wrapped in a try{...}catch() block. For ease you can simply put each PDO call into a try {... } wrapper and then catch as follows:

try {
    /* Or whatever DB call you make */ 
    $this->_db->delete('users_session', array('user_id', '=', $this->data()->id)); 
} 
catch(\Exception $ex){
    error_log("An Exception was caught! :".print_r($ex,true));
}

It is usually easiest to simply put a catch all global Exception ( \Exception ) as exampled above, rather than a multitude of different specific exceptions, but the option is there in the code for once you're more familiar with this concept.

This will give you basic feedback when an action (such as your delete) fails, and why it failed (in this case written to your PHP error log).

This will not solve the core issue ( You're doing a fetchAll after a delete query. ) but will stop Fatal Errors being generated and breaking your application. You can then handle this more appropriately such as outputting a message to the user.

The PHP manual has a lot of useful background and structure on how to implement effective Exception handling in PHP.