[PHP/PDO类]致命错误：调用布尔值上的成员函数fetch（）

每当我尝试使用我的PDO数据库包装器从我的数据库中获取某些内容时，我都会收到此错误：

致命错误：调用第17行C:\xampp\htdocs\index.php中布尔值上的成员函数fetch（）
index.php

require_once 'class.db.php';
$mysql = [
    'hostname'  => '127.0.0.1',
    'database'  => 'lucidcms',
    'username'  => 'root',
    'password'  => 'test',
    'charset'   => 'utf8',
];
$db = new Database($mysql);

$u = "Sentinel";

$result = $db->prepare("SELECT `id` FROM `users` WHERE `username` = :u LIMIT 1")
             ->execute([':u' => $u])
             ->fetch();
echo $result;

<?php
class Database {

    private static $stmt, $pdo;

    public function __construct(array $mysql) {
        if(is_null(self::$pdo)) {
            try {
                self::$pdo = new \PDO(
                    'mysql:dbname='.$mysql['database'].';host='.$mysql['hostname'].';charset='.$mysql['charset'], 
                    $mysql['username'], 
                    $mysql['password'],
                    [\PDO::ATTR_ERRMODE => \PDO::ERRMODE_EXCEPTION, \PDO::ATTR_PERSISTENT => true]
                );
            } catch(PDOException $e) {
                die('An error occurred when trying to communicate with the database.');
                //die($e->getMessage());
            }
        } else {
            return new self;
        }
    }

    public function __destruct() {
        // Destruct the connection to DB once finished
        try {
            self::$pdo = null;
        } catch(PDOException $e) {
            die('An error occurred when trying to close the connection with the database.');
            //die($e->getMessage());
        }
    }

    public static function prepare($sql) {
        self::$stmt = self::$pdo->prepare($sql);
        return self::$stmt;
    }

    public static function execute($data = []) {
        return self::$stmt->execute(isset($data) ? $data : null);
    }

    public static function count() {
        return self::$stmt->rowCount();
    }

    public static function fetch() {
        return self::$stmt->fetchColumn();
    }

    public static function fetchAll($type = \PDO::FETCH_ASSOC) {
        return self::$stmt->fetch($type);
    }

    public static function lastId() {
        return self::$pdo->lastInsertId();
    }

}

class.db.php

require_once 'class.db.php';
$mysql = [
    'hostname'  => '127.0.0.1',
    'database'  => 'lucidcms',
    'username'  => 'root',
    'password'  => 'test',
    'charset'   => 'utf8',
];
$db = new Database($mysql);

$u = "Sentinel";

$result = $db->prepare("SELECT `id` FROM `users` WHERE `username` = :u LIMIT 1")
             ->execute([':u' => $u])
             ->fetch();
echo $result;

<?php
class Database {

    private static $stmt, $pdo;

    public function __construct(array $mysql) {
        if(is_null(self::$pdo)) {
            try {
                self::$pdo = new \PDO(
                    'mysql:dbname='.$mysql['database'].';host='.$mysql['hostname'].';charset='.$mysql['charset'], 
                    $mysql['username'], 
                    $mysql['password'],
                    [\PDO::ATTR_ERRMODE => \PDO::ERRMODE_EXCEPTION, \PDO::ATTR_PERSISTENT => true]
                );
            } catch(PDOException $e) {
                die('An error occurred when trying to communicate with the database.');
                //die($e->getMessage());
            }
        } else {
            return new self;
        }
    }

    public function __destruct() {
        // Destruct the connection to DB once finished
        try {
            self::$pdo = null;
        } catch(PDOException $e) {
            die('An error occurred when trying to close the connection with the database.');
            //die($e->getMessage());
        }
    }

    public static function prepare($sql) {
        self::$stmt = self::$pdo->prepare($sql);
        return self::$stmt;
    }

    public static function execute($data = []) {
        return self::$stmt->execute(isset($data) ? $data : null);
    }

    public static function count() {
        return self::$stmt->rowCount();
    }

    public static function fetch() {
        return self::$stmt->fetchColumn();
    }

    public static function fetchAll($type = \PDO::FETCH_ASSOC) {
        return self::$stmt->fetch($type);
    }

    public static function lastId() {
        return self::$pdo->lastInsertId();
    }

}

您做了很多错事，（仅完全更改了方法名称！）但是您得到的错误消息很清楚：如果您想使用方法链接，您应该像编写prepare（）一样编写每个方法，以使其返回语句

然而，这个类无法挽救，因为它会导致严重的生产错误，这是由于它的错误。让我建议另一种解决方案，它更轻量级，更不容易出错，而不是这种麻烦的混乱局面

class MyPDO extends PDO
{
    public function run($sql, $args = NULL)
    {
        $stmt = $this->prepare($sql);
        $stmt->execute($args);
        return $stmt;
    }
}

有了这个简单的扩展，您将能够在SELECT查询中使用方法链接，而不会有弄乱代码的风险

$result = $db->run("SELECT `id` FROM `users` WHERE `username` = :u LIMIT 1", [':u' => $u])
             ->fetch();

它不像您当前的方法那样整洁，但同样-它没有承受其可怕的缺点。
谢谢，我会检查它。那太糟糕了。Ikr，但我不是真的要使用它，它只是用于测试目的。哦，让我看看这个。