未捕获的错误：调用成员函数prepare()（PDO，php）

Question

我试图使用 PHP 中的公共函数从表中获取数据，但出现以下错误：未捕获的错误：调用成员函数prepare()（PDO，php）我搜索了 2、3 个小时...但没有类似的结果或者我不明白。<?phpclass Config {    public static $SQL;    private function __construct() {        $host_name = "localhost";        $base_user = "root";        $base_pass = "";        $base_name = "home_page";        try {            self::$SQL = new PDO("mysql:host=$host_name;dbname=$base_name", $base_user, $base_pass);            self::$SQL->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);            echo "Connected successfully";        } catch(PDOException $e) {            die("Something went wrong, database connection closed. Reason: ". $e->getMessage());        }    }    public static function GetData($table, $data, $id) {        $wc = Config::$SQL->prepare('SELECT `'.$data.'` FROM `'.$table.'` WHERE `ID` = ?');        $wc->execute(array($id));        $r_data = $wc->fetch();        return $r_data[$data];    }}?>我在我的基本文件中使用它：<h1><?php echo Config::GetData("page_details", "Moto", 1) ?></h1>错误来自这一行：$wc = self::$SQL->prepare('SELECT `'.$data.'` FROM `'.$table.'` WHERE `ID` = ?');

Answer 1

您想在任何地方使用有什么特殊原因吗STATIC？常见的方法是使用公共的动态方法和属性。我用 PHP OOP 中建议的命名约定重写了您的示例，它有效：

<?php

class Config

{

    /** @var PDO $conn */

    private $conn = null;

    public function __construct()

    {

        $host_name = "localhost";

        $base_user = "root";

        $base_pass = "";

        $base_name = "home_page";

        try {

            $this->conn = new PDO("mysql:host=$host_name;dbname=$base_name", $base_user, $base_pass);

            $this->conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

            echo "Connected successfully"; // <- this is unnnesesary

        } catch (PDOException $e) {

            die("Something went wrong, database connection closed. Reason: " . $e->getMessage());

        }

    }

    public function findById($table, $data, $id)

    {

        $stmt = $this->conn->prepare('SELECT `' . $data . '` FROM `' . $table . '` WHERE `uid` = ?');

        $stmt->execute(array($id));

        return  $stmt->fetch(PDO::FETCH_ASSOC);

    }

}

// just for test

$cfg = new Config();

print_r($cfg->findById('foo', '*', 1));

或者在你的情况下

<?php echo $cfg->findById("page_details", "Moto", 1)['Moto'] ?>