Question

我对PHP非常熟悉，但我刚开始用它做一些面向对象的东西。我想建立一个单例数据库连接，但我遇到了一个问题和错误。“致命错误：允许的内存大小为134217728字节耗尽（试图分配523800字节）” 我知道我运行的查询不应该耗尽内存

$con = getConnection();
$stmt = $con->prepare("SELECT gene_name,jgi_protein_id FROM   jgi_transcriptid_proteinid_match where our_protein_id = ?");

以下是该课程的代码。

class Connection
{
    // Store the single instance of connection 
    private static $connection;

    private function __construct()
    {
        $connection = new mysqli(HOSTNAME, DBUSER, PASSWORD, DBNAME);

        if ($connection->connect_errno)
            die("Failed to connect to MySQL: (" . $connection->connect_errno . ") " . $connection->connect_error);
    }

    public static function getInstance() 
    { 
        if (!self::$connection) 
            self::$connection = new Connection(); 

        return self::$connection; 
    }

    public function prepare($query) 
    {
        $statement = $this->prepare($query);
        return $statement; 
    }
}

我正在使用mysqli作为数据库的东西。

Answer 1

此代码中存在几个问题：

无限递归

public function prepare($query) 
{
  $statement = $this->prepare($query);
  return $statement; 
}

引用局部变量，而不是静态变量
代码可能应该引用self::$connection。但是，基于课程，我不确定，self::$connection在getInstance()中以不同的方式使用，我看不到任何地方。

private function __construct()
    {
        $connection = new mysqli(HOSTNAME, DBUSER, PASSWORD, DBNAME);

        if ($connection->connect_errno)
            die("Failed to connect to MySQL: (" . $connection->connect_errno . ") " . $connection->connect_error);
    }

命名混淆
该类称为Connection，它包含一个名为$connection的静态变量，它存储该类的单例实例。构造函数包含另一个$connection，而不是 mysqli 连接。

重构类 - 未完成修复
下面的课程尚未经过测试，仅供参考。使用风险自负。

class Connection { //存储类的单个实例 private static $ instance; //存储mysqli连接私人$连接;

public function __construct() {
    // NOTE: it would be better to pass connection parameters as arguments
    $this->connection = new mysqli(HOSTNAME, DBUSER, PASSWORD, DBNAME);

    if ($this->connection->connect_errno)
        die("Failed to connect to MySQL: (" . $this->connection->connect_errno . ") " . $this->connection->connect_error);
}

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

    return self::$instance; 
}

public function prepare($query) {
    $statement = $this->connection->prepare($query);
    return $statement; 
}

}

致命错误：由于代码错误导致php中允许的内存大小错误

1 个答案: