Question

我无法弄清楚为什么我会继续犯两个错误。

注意：未定义的变量：第8行的C：\ xampp \ htdocs ...... index.php中的用户名

致命错误：无法访问第8行的C：\ xampp \ htdocs ....... index.php中的空属性

Heres my DB CLASS


<?php
class DB {
private static $_instance = null;
private   $_pdo, 
        $_query, 
        $_error = false,
        $_results,
        $_count = 0;

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'));
    }catch(PDOException $e){
        die($e->getMessage());
    }
}

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

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

public function results(){
    return $this->_results;
}   

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

public function count() {
    return $this->_count;
}

这是我的index.php

<?php
require_once 'core/init.php';
$user = DB::getInstance()->get('users', array('username', '=', 'alex'));
if(!$user->count()) {
    echo 'No User';
    } else {
        foreach($user->results() as $user) {
        echo $user->$username, '<br>';
    }
}

与我的数据库的连接正常，我的准备工作成功，我的bindValue成功运行，我的计数方法也正常，如果我尝试从db中获取不存在的用户，则返回false /'No User'，但是当我使用foreach回应实际的用户名时，我得到了那两个错误，这就是我被困住的地方。因为$ user是由getInstance定义的，不应该定义$ username，因此不是空属性？

Answer 1

您想致电$user->username而不是$user->$username。

<?php
require_once 'core/init.php';
$user = DB::getInstance()->get('users', array('username', '=', 'alex'));
if(!$user->count()) {
    echo 'No User';
    } else {
        foreach($user->results() as $user) {
        echo $user->username, '<br>';
    }
}

我无法在OOP中回显用户名

1 个答案: