fetchall()之后的PDO fetchObject().返回假 [英] PDO fetchObject() after fetchall(). returning false

问题描述

我是PHP新手. 我试图以表格的形式显示员工的详细信息. 但是while($row = $result->fetchObject())部分未执行，因为$result->fetchObject()返回false.与$rows = $result->fetchAll();有关吗? 这是代码段.

I am new to PHP. I am trying to display the details of employees in form of table. But while($row = $result->fetchObject()) part is not executing, as $result->fetchObject() is returning false. Has it something to do with $rows = $result->fetchAll();? Here's the code snippet.

$sql = "SELECT id, name, designation FROM employees";

if ($result = $pdo->query($sql)) {
    $rows = $result->fetchAll();
    $num_rows = count($rows);

    if ($num_rows > 0) {
        echo "<table>\n";
        echo " <tr class=\"heading\">\n";
        echo " <td>ID</td>\n";
        echo " <td>Name</td>\n";
        echo " <td>Designation</td>\n";    
        echo " </tr>\n";

        while($row = $result->fetchObject()) {
            echo " <tr>\n";
            echo " <td>" . $row->id . "</td>\n";
            echo " <td>" . $row->name . "</td>\n";
            echo " <td>" . $row->designation . "</td>\n";
            echo " </tr>\n";
        }
        echo "</table>";
    } else {
        echo "No employees in database.";
    }

else {
    echo "ERROR: Could not execute $sql. " . print_r
    ($pdo->errorInfo());
}

推荐答案

PDO的文档对此有些困惑，但是

PDO's documentation is a little confusing on this, but the PDOStatement::fetch() method and its cousin fetchAll() return false when no more rows are available to return. The docs say it returns false on failure, and a lack of available rows counts as a failure.

您对fetchAll()的初始调用从PDOstatement结果对象获取所有行，并且fetchObject()调用不再需要检索，因此它返回false.

Your initial call to fetchAll() gets all the rows from the PDOstatement result object and there are no more for the fetchObject() call to retrieve so it returns false.

您只需要初始调用fetchAll()，但是如果您之前未为连接设置默认的提取类型，则可能需要将其提取类型设置为PDO::FETCH_OBJ.

You only need your initial call to fetchAll(), but you may need to set its fetch type to PDO::FETCH_OBJ if you did not previously set the default fetch type for your connection.

然后，可以在已有的$rows数组上用简单的foreach循环替换while循环.这具有将显示逻辑与数据库查询业务逻辑分开的更多好处:

Then, you can replace your while loop with a simple foreach loop over the $rows array you already have. This has the added benefit of separating your display logic from your database query business logic a little more:

if ($result = $pdo->query($sql)) {
    // Fetch them now, as objects
    $rows = $result->fetchAll(PDO::FETCH_OBJ);
    $num_rows = count($rows);

    if ($num_rows > 0) {
        echo "<table>\n";
        echo " <tr class=\"heading\">\n";
        echo " <td>ID</td>\n";
        echo " <td>Name</td>\n";
        echo " <td>Designation</td>\n";    
        echo " </tr>\n";

        // $rows now has everything you need, just loop over it
        foreach ($rows as $row {
            echo " <tr>\n";
            echo " <td>" . htmlspecialchars($row->id) . "</td>\n";
            echo " <td>" . htmlspecialchars($row->name) . "</td>\n";
            echo " <td>" . htmlspecialchars($row->designation) . "</td>\n";
            echo " </tr>\n";
        }
        echo "</table>";
    } else {
        echo "No employees in database.";
    }

else {
    echo "ERROR: Could not execute $sql. " . print_r
    ($pdo->errorInfo());
}

还请注意，我在将输出写入HTML时向htmlspecialchars()添加了调用.始终建议这样做，以便对< > &这样在HTML中具有特殊含义的字符进行正确编码，如果这些值是作为用户输入产生的，则可以避免跨站点脚本漏洞.

Note also, that I added calls to htmlspecialchars() while writing output to HTML. That is always recommended, so that characters like < > & which have special meaning in HTML are properly encoded, and avoids cross-site scripting vulnerabilities if those values originated as user input.

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