扩展PDO类

Question

下面是我到目前为止出来的数据库连接类，但我会通过扩展PDO类本身进行改进，

<?php 
class database 
{ 
    protected $connection = null; 

    #make a connection 
    public function __construct($hostname,$dbname,$username,$password) 
    { 
     try 
     { 
      # MySQL with PDO_MYSQL 
      $this->connection = new PDO("mysql:host=$hostname;dbname=$dbname", $username, $password); 
      $this->connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 
     } 
     catch (PDOException $e) 
     { 
      $this->connection = null; 
      die($e->getMessage()); 
     } 
    } 

    #get the number of rows in a result 
    public function num_rows($query) 
    { 
     # create a prepared statement 
     $stmt = $this->connection->prepare($query); 

     if($stmt) 
     { 
      # execute query 
      $stmt->execute(); 

      return $stmt->rowCount(); 
     } 
     else 
     { 
      return self::get_error(); 
     } 
    } 

    #display error 
    public function get_error() 
    { 
     $this->connection->errorInfo(); 
    } 

    # closes the database connection when object is destroyed. 
    public function __destruct() 
    { 
     $this->connection = null; 
    } 
} 
?> 

扩展类，

class database extends PDO 
{ 

    #make a connection 
    public function __construct($hostname,$dbname,$username,$password) 
    { 
     parent::__construct($hostname,$dbname,$username,$password); 

     try 
     { 
      $this->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 
     } 
     catch (PDOException $e) 
     { 
      die($e->getMessage()); 
     } 
    } 

    #get the number of rows in a result 
    public function num_rows($query) 
    { 
     # create a prepared statement 
     $stmt = parent::prepare($query); 

     if($stmt) 
     { 
      # execute query 
      $stmt->execute(); 

      return $stmt->rowCount(); 
     } 
     else 
     { 
      return self::get_error(); 
     } 
    } 

    #display error 
    public function get_error() 
    { 
     $this->connection->errorInfo(); 
    } 

    # closes the database connection when object is destroyed. 
    public function __destruct() 
    { 
     $this->connection = null; 
    } 
} 

这是我如何实例化类，

# the host used to access DB 
define('DB_HOST', 'localhost'); 

# the username used to access DB 
define('DB_USER', 'root'); 

# the password for the username 
define('DB_PASS', 'xxx'); 

# the name of your databse 
define('DB_NAME', 'db_2011'); 

include 'class_database.php'; 

$connection = new database(DB_HOST,DB_NAME,DB_USER,DB_PASS); 
$sql = " 
    SELECT * 
    FROM root_contacts_cfm 
    ORDER BY cnt_id DESC 
    "; 

$connection->num_rows($sql); 

但我有错误，当我把这个扩展PDO类，

Warning: PDO::__construct() expects parameter 4 to be array, string given in C:\wamp\www\xx\class_database.php on line xx

Fatal error: Call to a member function setAttribute() on a non-object in C:\wamp\www\xx\class_database.php on line xx

我已经做了一些研究，在网上，我发现扩展PDO的这个基本结构，但我不明白它...

class myPDO extends PDO 
{ 
    public function __construct($dsn, 
           $username=null, 
           $password=null, 
           $driver_options=null) 
    { 
     parent::__construct($dsn, $username, $password, $driver_options); 
    } 

    public function query($query) 
    { 
     $result = parent::query($query); 
     // do other stuff you want to do here, then... 
     return($result); 
    } 
} 

什么是$ds N个变量的呢？如何将我的$hostname变量传递给扩展的pdo类？

另一个问题： 如何在扩展的pdo类中显示错误的方法？ 如何关闭扩展的pdo类中的连接？

从mysqli移动到pdo是非常困难的！

谢谢。

Answer 1

$ dsn是数据源名称。它为你处理你的主机名。您可以使用这样的：

$dsn = 'mysql:dbname=YOUR_DB_NAME;host=YOUR_HOSTNAME' 

随着$this->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);您已设置例外线的时候发生错误（我喜欢）待提高，所以在您的扩展类，您可以处理在异常处理程序错误。如果您在扩展PDO类有一个名为getAssoc方法则是这样的：

/// Get an associative array of results for the sql. 
public function getAssoc($sql, $params=array()) 
{ 
    try 
    { 
     $stmt = $this->prepare($sql); 
     $params = is_array($params) ? $params : array($params); 
     $stmt->execute($params); 

     return $stmt->fetchAll(PDO::FETCH_ASSOC); 
    } 
    catch (Exception $e) 
    { 
     // Echo the error or Re-throw it to catch it higher up where you have more 
     // information on where it occurred in your program. 
     // e.g echo 'Error: ' . $e->getMessage(); 

     throw new Exception(
      __METHOD__ . 'Exception Raised for sql: ' . var_export($sql, true) . 
      ' Params: ' . var_export($params, true) . 
      ' Error_Info: ' . var_export($this->errorInfo(), true), 
      0, 
      $e); 
    } 
} 

Answer 2

我会集中在哪些类需要做的，而不是试图重新写PDO。我有同样的想法，因为我虽然会简化代码，但它不会。你最终花更多的时间研究如何间接与PDO接口。