我正在考虑在未来的所有webapp中使用PDO。目前（使用我迄今为止从SO中学到的东西），我在我的网站中处理数据库连接的是一个像这样的Singleton类：
class DB {
private static $instance = NULL;
private static $dsn = "mysql:host=localhost;dbname=mydatabase;";
private static $db_user = 'root';
private static $db_pass = '0O0ooIl1';
private function __construct()
{
}
private function __clone()
{
}
public static function getInstance() {
if (!self::$instance)
{
self::$instance = new PDO(self::$dsn, self::$db_user, self::$db_pass);
self::$instance-> setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
return self::$instance;
}
}
和另一个具有内容特定功能的文件（functions.php）与此完全相同：
function get_recent_activities ()
{
try
{
$db = DB::getInstance();
// --prepare and execute query here, fetch the result--
return $my_list_of_recent_activities;
}
catch (PDOException $e)
{
return "some fail-messages";
}
}
...
意思是我必须在所有函数中重复try .. catch部分。
我的问题是：
try..catch，但仍然能够在每个功能上返回不同的“失败消息”）如果这看起来不清楚或太长，我很抱歉。提前谢谢。
答案 0 :(得分：40)
您的实施很好，并且它在大多数情况下都能很好地工作。
没有必要将每个查询放在try / catch块中，事实上在大多数情况下你实际上并不想这样做。这样做的原因是，如果查询生成异常，则是语法错误或数据库问题等致命问题的结果，并且这些问题不是您应该对每个查询进行说明的问题。
例如：
try {
$rs = $db->prepare('SELECT * FROM foo');
$rs->execute();
$foo = $rs->fetchAll();
} catch (Exception $e) {
die("Oh noes! There's an error in the query!");
}
此处的查询将正常工作或根本不工作。它根本不起作用的情况不应该在生产系统上有任何规律性，因此它们不是你应该在这里检查的条件。这样做实际上会适得其反，因为您的用户会收到永远不会改变的错误，并且您不会收到提醒您解决问题的异常消息。
相反，只需写下：
$rs = $db->prepare('SELECT * FROM foo');
$rs->execute();
$foo = $rs->fetchAll();
通常，您唯一想要捕获和处理查询异常的时间是在查询失败时要执行其他操作的时间。例如：
// We're handling a file upload here.
try {
$rs = $db->prepare('INSERT INTO files (fileID, filename) VALUES (?, ?)');
$rs->execute(array(1234, '/var/tmp/file1234.txt'));
} catch (Exception $e) {
unlink('/var/tmp/file1234.txt');
throw $e;
}
您需要编写一个简单的异常处理程序，记录或通知您生产环境中发生的数据库错误，并向用户显示友好的错误消息，而不是异常跟踪。有关如何执行此操作的信息，请参阅http://www.php.net/set-exception-handler。
答案 1 :(得分：3)
这里有几点需要注意：
哦，我应该指出，这一点说明了如何包装单个函数来处理查询的所有异常处理。我现在几乎不在其他任何地方编写try catch块，因为查询中的堆栈跟踪为我提供了调试问题并修复它所需的所有信息。
这是我当前的PDO包装器类实现：
class DB extends PDO
{
// Allows implementation of the singleton pattern -- ndg 5/24/2008
private static $instance;
// Public static variables for configuring the DB class for a particular database -- ndg 6/16/2008
public static $error_table;
public static $host_name;
public static $db_name;
public static $username;
public static $password;
public static $driver_options;
public static $db_config_path;
function __construct($dsn="", $username="", $password="", $driver_options=array())
{
if(isset(self::$db_config_path))
{
try
{
if(!require_once self::$db_config_path)
{
throw new error('Failed to require file: ' . self::$db_config_path);
}
}
catch(error $e)
{
$e->emailAdmin();
}
}
elseif(isset($_ENV['DB']))
{
self::$db_config_path = 'config.db.php';
try
{
if(!require_once self::$db_config_path)
{
throw new error('Failed to require file: ' . self::$db_config_path);
}
}
catch(error $e)
{
$e->emailAdmin();
}
}
parent::__construct("mysql:host=" . self::$host_name . ";dbname=" .self::$db_name, self::$username, self::$password, self::$driver_options);
$this->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$this->setAttribute(PDO::ATTR_STATEMENT_CLASS, array('QueryStatement', array($this)));
if(!isset(self::$error_table))
{
self::$error_table = 'errorlog_rtab';
}
}
/**
* Return a DB Connection Object
*
* @return DB
*/
public static function connect()
{
// New PDO Connection to be used in NEW development and MAINTENANCE development
try
{
if(!isset(self::$instance))
{
if(!self::$instance = new DB())
{
throw new error('PDO DB Connection failed with error: ' . self::errorInfo());
}
}
return self::$instance;
}
catch(error $e)
{
$e->printErrMsg();
}
}
/**
* Returns a QueryBuilder object which can be used to build dynamic queries
*
* @return QueryBuilder
*
*/
public function createQuery()
{
return new QueryBuilder();
}
public function executeStatement($statement, $params = null, $FETCH_MODE = null)
{
if($FETCH_MODE == 'scalar')
{
return $this->executeScalar($statement, $params);
}
try {
try {
if(!empty($params))
{
$stmt = $this->prepare($statement);
$stmt->execute($params);
}
else
{
$stmt = $this->query($statement);
}
}
catch(PDOException $pdo_error)
{
throw new error("Failed to execute query:\n" . $statement . "\nUsing Parameters:\n" . print_r($params, true) . "\nWith Error:\n" . $pdo_error->getMessage());
}
}
catch(error $e)
{
$this->logDBError($e);
$e->emailAdmin();
return false;
}
try
{
if($FETCH_MODE == 'all')
{
$tmp = $stmt->fetchAll();
}
elseif($FETCH_MODE == 'column')
{
$arr = $stmt->fetchAll();
foreach($arr as $key => $val)
{
foreach($val as $var => $value)
{
$tmp[] = $value;
}
}
}
elseif($FETCH_MODE == 'row')
{
$tmp = $stmt->fetch();
}
elseif(empty($FETCH_MODE))
{
return true;
}
}
catch(PDOException $pdoError)
{
return true;
}
$stmt->closeCursor();
return $tmp;
}
public function executeScalar($statement, $params = null)
{
$stmt = $this->prepare($statement);
if(!empty($this->bound_params) && empty($params))
{
$params = $this->bound_params;
}
try {
try {
if(!empty($params))
{
$stmt->execute($params);
}
else
{
$stmt = $this->query($statement);
}
}
catch(PDOException $pdo_error)
{
throw new error("Failed to execute query:\n" . $statement . "\nUsing Parameters:\n" . print_r($params, true) . "\nWith Error:\n" . $pdo_error->getMessage());
}
}
catch(error $e)
{
$this->logDBError($e);
$e->emailAdmin();
}
$count = $stmt->fetchColumn();
$stmt->closeCursor();
//echo $count;
return $count;
}
protected function logDBError($e)
{
$error = $e->getErrorReport();
$sql = "
INSERT INTO " . self::$error_table . " (message, time_date)
VALUES (:error, NOW())";
$this->executeStatement($sql, array(':error' => $error));
}
}
class QueryStatement extends PDOStatement
{
public $conn;
protected function __construct()
{
$this->conn = DB::connect();
$this->setFetchMode(PDO::FETCH_ASSOC);
}
public function execute($bound_params = null)
{
return parent::execute($bound_params);
}
}