phpoop&；PDO从mysql获取数据

我正在学习OOP和PDO，我为数据库编写了类，为用户编写了类。我编写了注册方法（我想是正确的），所以现在我想获取所有用户的数据，并使用这个公共变量，它们在我的类中

class Database{
    private static $_instance = null;
    private $_pdo,
            $_error = false,
            $_query,
            $_results,
            $_count;

    private function __construct(){
        try{
            $this->_pdo = new PDO('mysql:host='.HOST.';dbname='.DBNAME,USERNAME,PASSWORD);
        }catch(PDOExeption $e){
            die($e->getMessage());
        }
    }

    public static function getInstance(){
        if(!isset(self::$_instance)){
            self::$_instance = new Database();
        }
        return self::$_instance;
    }

    public function query($sql, $params = array()){
        $this->_error = false;
        $bindParamCounter = 1;
        if($this->_query = $this->_pdo->prepare($sql)){
            if(count($params)){
                foreach ($params as $value) {
                    $this->_query->bindValue($bindParamCounter, $value);
                    $bindParamCounter++;
                }
            }
            if($this->_query->execute()){
                $this->_results = $this->_query->fetchAll(PDO::FETCH_OBJ);
            }else{
                $this->_error = true;
            }
        }
        return $this;
    }

    public function insert($table, $params = array()){

        $paramsCounter = count($params);

            if($paramsCounter > 0){
                $i = 0;

                for($i = 0; $i < $paramsCounter; $i++){
                    $questionMarks[] =  '?';
                }

                    $paramsKeys = implode(', ', array_keys($params));
                    $questionMarks =  implode(', ', $questionMarks);
                    $sql =  'INSERT INTO '. $table.'('.$paramsKeys.')'." VALUES ({$questionMarks})";

            }
        return $this->query($sql, $params);
    }

    public function error(){
        return $this->_error;
    }

---

有人能帮我吗？

使用您编写的查询方法？您到底遇到了什么问题？你看过PDO库的文档了吗？（例如，像这样）当异常发生时，不要让它轻易消亡。

class Users{
    private $_pdo,
            $_data,
            $_userID,
            $_userPassword;

    public $id;
    public $username;
    public $password;
    public $firstname;
    public $last_name;

    public function __construct($user = NULL){
        $this->_pdo = Database::getInstance();
    }

    public function create($params = array()){
        try{
            $this->_pdo->insert('users', $params);
        }catch(PDOExeption $e){
            die($e->getMessage());
        }
    }

    public function getAllUsers(){
        //get all users
    }
}