简体中文
简体中文
PDO 类提供了一个构造函数 __construct，它用于创建一个到数据库的连接。使用此构造函数时，你需要传递以下几个参数：
dsn（Data Source Name）：包含连接信息的字符串，如数据库类型、主机名、数据库名等。
username：数据库用户名。
password：数据库密码。
options（可选）：PDO 提供了一些配置选项，如设置错误模式、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> => PDO::</span><span><span class="hljs-variable constant_">ERRMODE_EXCEPTION</span></span><span>, </span><span><span class="hljs-comment">// 设置错误处理模式为异常</span></span><span>
PDO::</span><span><span class="hljs-variable constant_">ATTR_DEFAULT_FETCH_MODE</span></span><span> => PDO::</span><span><span class="hljs-variable constant_">FETCH_ASSOC</span></span><span>, </span><span><span class="hljs-comment">// 设置默认取回数据的方式</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">$e</span></span><span>-></span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>();
}
</span></span>在这个例子中，我们传递了一个 DSN 字符串来连接 MySQL 数据库，并设置了错误处理模式。
默认情况下，PDO 的错误处理模式是 PDO::ERRMODE_SILENT，也就是不抛出异常，而是返回一个错误代码。因此，当你发生错误时，程序不会自动抛出异常，你需要显式地检查错误代码并做出处理。这可能导致一些潜在的错误被忽略，从而使得问题难以排查。
为了让代码更加健壮，建议将错误处理模式设置为 PDO::ERRMODE_EXCEPTION，这意味着 PDO 会在发生错误时抛出一个 PDOException 异常。这样，你可以通过 try-catch 结构来捕获并处理异常。
<span><span><span class="hljs-variable">$options</span></span><span> = [
PDO::</span><span><span class="hljs-variable constant_">ATTR_ERRMODE</span></span><span> => PDO::</span><span><span class="hljs-variable constant_">ERRMODE_EXCEPTION</span></span><span>, </span><span><span class="hljs-comment">// 设置为抛出异常</span></span><span>
PDO::</span><span><span class="hljs-variable constant_">ATTR_DEFAULT_FETCH_MODE</span></span><span> => 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">$e</span></span><span>-></span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>();
}
</span></span>在上面的代码中，PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION 设置了当发生错误时，PDO 会抛出异常 PDOException。通过 catch 块捕获异常并处理，可以避免程序崩溃并输出有用的错误信息。
PDO::ERRMODE_EXCEPTION 会导致数据库操作发生异常时自动抛出 PDOException 异常。你可以在 try-catch 语句中捕获这些异常。
<span><span><span class="hljs-keyword">try</span></span><span> {
</span><span><span class="hljs-variable">$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">// 执行数据库操作</span></span><span>
} </span><span><span class="hljs-keyword">catch</span></span><span> (PDOException </span><span><span class="hljs-variable">$e</span></span><span>) {
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">'数据库连接错误: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-></span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>();
}
</span></span>在 catch 语句中，我们通过 $e->getMessage() 获取异常的详细信息，这对调试和记录日志非常重要。
除了在界面上显示错误信息外，建议将异常信息记录到日志中，以便进行后续的分析和排查。你可以使用 PHP 的 error_log() 函数或集成像 Monolog 这样的日志库来记录这些信息。
<span><span><span class="hljs-keyword">try</span></span><span> {
</span><span><span class="hljs-variable">$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">$e</span></span><span>) {
</span><span><span class="hljs-title function_ invoke__">error_log</span></span><span>(</span><span><span class="hljs-string">'数据库连接错误: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-></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">'数据库连接失败，请稍后重试！'</span></span><span>;
}
</span></span>如果用户名或密码不正确，PDO 会抛出 PDOException 异常，错误信息通常包含 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">'数据库连接错误: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-></span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>(); </span><span><span class="hljs-comment">// 输出“Access denied”错误</span></span><span>
}
</span></span>如果你指定的数据库不存在，PDO 会抛出类似 Unknown database 'testdb' 的错误。
<span><span><span class="hljs-keyword">try</span></span><span> {
</span><span><span class="hljs-variable">$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">$e</span></span><span>) {
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">'数据库连接错误: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-></span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>(); </span><span><span class="hljs-comment">// 输出“Unknown database”错误</span></span><span>
}
</span></span>如果数据库服务器不可用或连接超时，PDO 会抛出连接相关的异常。
<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">'数据库连接错误: '</span></span><span> . </span><span><span class="hljs-variable">$e</span></span><span>-></span><span><span class="hljs-title function_ invoke__">getMessage</span></span><span>(); </span><span><span class="hljs-comment">// 输出“Could not find driver”或“Connection timed out”</span></span><span>
}
</span></span>相关标签:
PDO
