PDO fetchObject() after fetchall(). returning false - php

Question

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());
}

Answer 1

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.
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.
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.
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());
}
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.