PDO::__construct 如何處理異常和錯誤？讓你的代碼更健壯的處理方案

gitbox 2025-09-04

1. PDO::__construct 方法簡介

PDO 類提供了一個構造函數__construct ，它用於創建一個到數據庫的連接。使用此構造函數時，你需要傳遞以下幾個參數：

dsn （Data Source Name）：包含連接信息的字符串，如數據庫類型、主機名、數據庫名等。
username ：數據庫用戶名。
password ：數據庫密碼。
options （可選）：PDO 提供了一些配置選項，如設置錯誤模式、字符集等。

例如：

 <span><span><span class="hljs-variable">$dsn</span></span><span> = </span><span><span class="hljs-string">'mysql:host=localhost;dbname=testdb'</span></span><span>;
</span><span><span class="hljs-variable">$username</span></span><span> = </span><span><span class="hljs-string">'root'</span></span><span>;
</span><span><span class="hljs-variable">$password</span></span><span> = </span><span><span class="hljs-string">''</span></span><span>;
</span><span><span class="hljs-variable">$options</span></span><span> = [
    PDO::</span><span><span class="hljs-variable constant_">ATTR_ERRMODE</span></span><span> =&gt; PDO::</span><span><span class="hljs-variable constant_">ERRMODE_EXCEPTION</span></span><span>, </span><span><span class="hljs-comment">// 設置錯誤處理模式為異常</span></span><span>
    PDO::</span><span><span class="hljs-variable constant_">ATTR_DEFAULT_FETCH_MODE</span></span><span> =&gt; PDO::</span><span><span class="hljs-variable constant_">FETCH_ASSOC</span></span><span>, </span><span><span class="hljs-comment">// 設置默認取回數據的方式</span></span><span>
];

</span><span><span class="hljs-keyword">try</span></span><span> {
    </span><span><span class="hljs-variable">$pdo</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title function_ invoke__">PDO</span></span><span>(</span><span><span class="hljs-variable">$dsn</span></span><span>, </span><span><span class="hljs-variable">$username</span></span><span>, </span><span><span class="hljs-variable">$password</span></span><span>, </span><span><span class="hljs-variable">$options</span></span><span>);
} </span><span><span class="hljs-keyword">catch</span></span><span> (PDOException </span><span><span class="hljs-variable">$e</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">'Connection failed: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>();
}
</span></span>

在這個例子中，我們傳遞了一個DSN 字符串來連接MySQL 數據庫，並設置了錯誤處理模式。

2. 錯誤處理模式：設置為異常（ PDO::ERRMODE_EXCEPTION ）

默認情況下，PDO 的錯誤處理模式是PDO::ERRMODE_SILENT ，也就是不拋出異常，而是返回一個錯誤代碼。因此，當你發生錯誤時，程序不會自動拋出異常，你需要顯式地檢查錯誤代碼並做出處理。這可能導致一些潛在的錯誤被忽略，從而使得問題難以排查。

為了讓代碼更加健壯，建議將錯誤處理模式設置為PDO::ERRMODE_EXCEPTION ，這意味著PDO 會在發生錯誤時拋出一個PDOException異常。這樣，你可以通過try-catch結構來捕獲並處理異常。

設置錯誤模式為異常

<span><span><span class="hljs-variable">$options</span></span><span> = [
    PDO::</span><span><span class="hljs-variable constant_">ATTR_ERRMODE</span></span><span> =&gt; PDO::</span><span><span class="hljs-variable constant_">ERRMODE_EXCEPTION</span></span><span>, </span><span><span class="hljs-comment">// 設置為拋出異常</span></span><span>
    PDO::</span><span><span class="hljs-variable constant_">ATTR_DEFAULT_FETCH_MODE</span></span><span> =&gt; PDO::</span><span><span class="hljs-variable constant_">FETCH_ASSOC</span></span><span>,
];

</span><span><span class="hljs-keyword">try</span></span><span> {
    </span><span><span class="hljs-variable">$pdo</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title function_ invoke__">PDO</span></span><span>(</span><span><span class="hljs-variable">$dsn</span></span><span>, </span><span><span class="hljs-variable">$username</span></span><span>, </span><span><span class="hljs-variable">$password</span></span><span>, </span><span><span class="hljs-variable">$options</span></span><span>);
} </span><span><span class="hljs-keyword">catch</span></span><span> (PDOException </span><span><span class="hljs-variable">$e</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">'Connection failed: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>();
}
</span></span>

在上面的代碼中， PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION設置了當發生錯誤時，PDO 會拋出異常PDOException 。通過catch塊捕獲異常並處理，可以避免程序崩潰並輸出有用的錯誤信息。

3. 如何捕獲並處理PDO 異常

捕獲異常

PDO::ERRMODE_EXCEPTION會導致數據庫操作發生異常時自動拋出PDOException異常。你可以在try-catch語句中捕獲這些異常。

 <span><span><span class="hljs-keyword">try</span></span><span> {
    </span><span><span class="hljs-variable">$pdo</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title function_ invoke__">PDO</span></span><span>(</span><span><span class="hljs-variable">$dsn</span></span><span>, </span><span><span class="hljs-variable">$username</span></span><span>, </span><span><span class="hljs-variable">$password</span></span><span>, </span><span><span class="hljs-variable">$options</span></span><span>);
    </span><span><span class="hljs-comment">// 執行數據庫操作</span></span><span>
} </span><span><span class="hljs-keyword">catch</span></span><span> (PDOException </span><span><span class="hljs-variable">$e</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">'數據庫連接錯誤: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>();
}
</span></span>

在catch語句中，我們通過$e->getMessage()獲取異常的詳細信息，這對調試和記錄日誌非常重要。

異常信息記錄

除了在界面上顯示錯誤信息外，建議將異常信息記錄到日誌中，以便進行後續的分析和排查。你可以使用PHP 的error_log()函數或集成像Monolog 這樣的日誌庫來記錄這些信息。

 <span><span><span class="hljs-keyword">try</span></span><span> {
    </span><span><span class="hljs-variable">$pdo</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title function_ invoke__">PDO</span></span><span>(</span><span><span class="hljs-variable">$dsn</span></span><span>, </span><span><span class="hljs-variable">$username</span></span><span>, </span><span><span class="hljs-variable">$password</span></span><span>, </span><span><span class="hljs-variable">$options</span></span><span>);
} </span><span><span class="hljs-keyword">catch</span></span><span> (PDOException </span><span><span class="hljs-variable">$e</span></span><span>) {
    </span><span><span class="hljs-title function_ invoke__">error_log</span></span><span>(</span><span><span class="hljs-string">'數據庫連接錯誤: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>());
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">'數據庫連接失敗，請稍後重試！'</span></span><span>;
}
</span></span>

4. 常見的數據庫連接錯誤及處理

錯誤1：用戶名或密碼錯誤

如果用戶名或密碼不正確，PDO 會拋出PDOException異常，錯誤信息通常包含Access denied 。

 <span><span><span class="hljs-keyword">try</span></span><span> {
    </span><span><span class="hljs-variable">$pdo</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title function_ invoke__">PDO</span></span><span>(</span><span><span class="hljs-string">'mysql:host=localhost;dbname=testdb'</span></span><span>, </span><span><span class="hljs-string">'invalid_user'</span></span><span>, </span><span><span class="hljs-string">'wrong_password'</span></span><span>);
} </span><span><span class="hljs-keyword">catch</span></span><span> (PDOException </span><span><span class="hljs-variable">$e</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">'數據庫連接錯誤: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>(); </span><span><span class="hljs-comment">// 輸出“Access denied”錯誤</span></span><span>
}
</span></span>

錯誤2：數據庫不存在

如果你指定的數據庫不存在，PDO 會拋出類似Unknown database 'testdb'的錯誤。

 <span><span><span class="hljs-keyword">try</span></span><span> {
    </span><span><span class="hljs-variable">$pdo</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title function_ invoke__">PDO</span></span><span>(</span><span><span class="hljs-string">'mysql:host=localhost;dbname=nonexistent_db'</span></span><span>, </span><span><span class="hljs-string">'root'</span></span><span>, </span><span><span class="hljs-string">''</span></span><span>);
} </span><span><span class="hljs-keyword">catch</span></span><span> (PDOException </span><span><span class="hljs-variable">$e</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">'數據庫連接錯誤: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>(); </span><span><span class="hljs-comment">// 輸出“Unknown database”錯誤</span></span><span>
}
</span></span>

錯誤3：數據庫服務器不可用

如果數據庫服務器不可用或連接超時，PDO 會拋出連接相關的異常。

 <span><span><span class="hljs-keyword">try</span></span><span> {
    </span><span><span class="hljs-variable">$pdo</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title function_ invoke__">PDO</span></span><span>(</span><span><span class="hljs-string">'mysql:host=nonexistent_host;dbname=testdb'</span></span><span>, </span><span><span class="hljs-string">'root'</span></span><span>, </span><span><span class="hljs-string">''</span></span><span>);
} </span><span><span class="hljs-keyword">catch</span></span><span> (PDOException </span><span><span class="hljs-variable">$e</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">'數據庫連接錯誤: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>(); </span><span><span class="hljs-comment">// 輸出“Could not find driver”或“Connection timed out”</span></span><span>
}
</span></span>

相關標籤:
PDO