与配置文件的单例数据库连接

Question

以下是我的连接代码，无需配置文件（.ini 文件）即可正常工作。但是如果我使用配置文件，我会收到错误：

致命错误： 常量表达式在第 13 行的 singletonDB.php 中包含无效操作。

但如您所见，变量$dsn、$user 和$pass 不是静态变量。我不明白为什么我会收到非静态变量的静态变量相关错误。

我的最终目标是使用配置文件以及只保持与 DB 的单例连接。

<?php
$config = parse_ini_file("config.ini");
var_dump($config);
// Singleton to connect db.
class ConnectDb
{

    // Hold the class instance.
    private static $instance = null;

    private $pdo;

    private $dsn = $config['dsn_config'];

    private $user = $config['user_config'];

    private $pass = $config['password_config'];

    // The db connection is established in the private constructor.
    private function __construct()
    {
        echo nl2br("Inside constructor"); 
        $this->pdo = new PDO($this->dsn, $this->user, $this->pass);
        $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    }

    public static function getInstance()
    {
        if (! self::$instance) {
            self::$instance = new ConnectDb();
        }

        return self::$instance;
    }

    public function getConnection()
    {
        return $this->pdo;
    }
}

这是我的配置文件

;Local
dsn_config = 'mysql:host=127.0.0.1;port=3306;dbname=db_name;';
user_config = 'root';
password_config = 'root';

谢谢。

Answer 1

问题不在于$dsn、$user 或$pass，而是$config。你不能这样分配$config。如果将它们更改为字符串或其他值（int、array、bool），您会发现错误消失了：

private $dsn  = false;  # All of these are 
private $user = [];     # are valid
private $pass = 1234;   # assignments

那么问题是如何分配ini 参数？一种常见的方法是在实例化时注入到类的构造中：

class ConnectDb
{
    private static $instance = null;

    private $pdo;    
    private $dsn = '';
    private $user = '';
    private $pass = '';

    private function __construct($dsn, $user, $pass)
    {
        $this->dns = $dns;
        $this->user = $user;
        $this->pass = $pass;

        echo nl2br("Inside constructor"); 
        $this->pdo = new PDO($this->dsn, $this->user, $this->pass);
        $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    }
    ...etc.

使用方法：

<?php
$config = parse_ini_file("config.ini");
# Inject into the construct here
$Db = new ConnectDb($config['dsn_config'], $config['user_config'], $config['password_config']);

另一种方法可能是使用定义（常量）：

<?php
$config = parse_ini_file("config.ini");
# Create some defines
define('DB_DSN', $config['dsn_config']);
define('DB_USER', $config['user_config']);
define('DB_PASS', $config['password_config']);

然后该类将如下所示：

class ConnectDb
{
    private static $instance = null;

    private $pdo;
    private $dsn = '';
    private $user = '';
    private $pass = '';

    private function __construct()
    {
        # Assign the constants here ALTHOUGH...
        # I don't know that there is a good reason to make these class 
        # variables. I would just put the constants into the construct of
        # the PDO below. I don't know that you are going to need to reference
        # these variables after you have created the PDO connection.
        $this->dns = DB_DSN;
        $this->user = DB_USER;
        $this->pass = DB_PASS;

        echo nl2br("Inside constructor"); 
        $this->pdo = new PDO($this->dsn, $this->user, $this->pass);
        $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    }
    ...etc.

Answer 2

我不想在程序的其他地方创建对象，因此根据@Rasclatt 的解释，我将配置读取代码移到了构造函数中，现在它工作正常。以下是更新后的代码。

文件名“singletonDB.php”

<?php

// Singleton to connect db.
class ConnectDB
{

    // Hold the class instance.
    private static $instance = null;

    private $pdo;

    private $dsn = '';

    private $user = '';

    private $pass = '';

    // The db connection is established in the private constructor.
    private function __construct()
    {
//         $pdo = new PDO($dsn, $user, $password);
        $config = parse_ini_file("../config.ini");
        echo nl2br("var_dump ing config");
        var_dump($config);

        $this->dsn = $config['dsn_config'];
        $this->user = $config['user_config'];
        $this->pass = $config['password_config'];

        echo nl2br("Inside constructor"); 
        $this->pdo = new PDO($this->dsn, $this->user, $this->pass);
        $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    }

    public static function getInstance()
    {
        if (! self::$instance) {
            self::$instance = new ConnectDB();
        }

        return self::$instance;
    }

    public function getConnection()
    {
        return $this->pdo;
    }
}

稍后你可以得到连接表单 DB as

require_once 'singletonDB.php';
$instance = ConnectDB::getInstance();
$conn = $instance->getConnection();
var_dump($conn);

但是我不确定这是否是一种好的编程方式。