fetch(PDO::FETCH_ASSOC) fails when it is called on a mysqli_result. PDO and mysqli are different database APIs: choose one and use its connection, result methods, constants and error handling consistently. If your result is from mysqli, call fetch_assoc(); if you want PDO fetch modes such as PDO::FETCH_ASSOC or PDO::FETCH_UNIQUE, create and query the database through PDO.
Identify the API mismatch
The characteristic error is similar to Call to undefined method mysqli_result::fetch(). That message means the query returned a mysqli result object, but the code attempted to use PDO’s fetch() method and constants on it. As a rule, do not combine the two APIs.
| Connection and result | Fetch code | Fetch-mode constants |
|---|---|---|
| PDO | $stmt->fetch(), $stmt->fetchAll() |
PDO::FETCH_ASSOC, PDO::FETCH_UNIQUE |
| mysqli | $result->fetch_assoc() |
Use mysqli’s result methods; PDO constants do not apply |
If the project uses mysqli
$result = $mysqli->query('SELECT id, pageheader, pagecontent FROM pages');
while ($row = $result->fetch_assoc()) {
echo htmlspecialchars($row['pageheader'], ENT_QUOTES, 'UTF-8');
}Keep the connection, query execution, result iteration and error handling in mysqli. Replacing only fetch() with a PDO constant will not convert a mysqli result into a PDO statement.
If the project uses PDO
$pdo = new PDO($dsn, $username, $password, [
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
]);
$stmt = $pdo->query(
'SELECT id, pageheader, pagecontent FROM pages'
);
while ($row = $stmt->fetch()) {
echo htmlspecialchars($row['pageheader'], ENT_QUOTES, 'UTF-8');
}Setting PDO::ATTR_DEFAULT_FETCH_MODE makes ordinary fetches associative without repeating PDO::FETCH_ASSOC on every call. You can still pass an explicit mode when a particular result needs a different shape.
#1 Best Overall
Create an array keyed by id with PDO
For a menu or lookup table keyed by page id, select the key column first and use fetchAll(PDO::FETCH_UNIQUE). The first selected column becomes each array key; the remaining selected columns become that key’s row value.
$stmt = $pdo->query(
'SELECT id, pageheader, pagecontent FROM pages ORDER BY id'
);
$pages = $stmt->fetchAll(PDO::FETCH_UNIQUE);
foreach ($pages as $id => $page) {
$url = 'index1.php?id=' . rawurlencode((string) $id);
echo '<a href="' . htmlspecialchars($url, ENT_QUOTES, 'UTF-8') . '">'
. htmlspecialchars($page['pageheader'], ENT_QUOTES, 'UTF-8')
. '</a>';
}With that query, a row such as id = 7 is available as $pages[7], while its values remain in $pages[7]['pageheader'] and $pages[7]['pagecontent']. If id is not the first selected column, another column will become the key instead.
Rank #2
Validate the requested page
$id = filter_input(INPUT_GET, 'id', FILTER_VALIDATE_INT);
if ($id === false || $id === null || !isset($pages[$id])) {
http_response_code(404);
exit('Page not found');
}
$page = $pages[$id];
echo htmlspecialchars($page['pagecontent'], ENT_QUOTES, 'UTF-8');This check prevents an absent or invalid id from becoming an undefined-array-key notice. For a large table, retrieving one page with a parameterized query is usually more efficient than loading every page into memory.
Why generated links may appear broken
Database fetching and navigation are separate problems. When a link does not work, inspect the HTML the browser received rather than only the PHP source. Use the browser’s View Source command and verify the rendered href, filename and query-string value.
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In the discussed example, links generated while the active script was index1.php pointed to index.php. Changing the target to the active filename restored the intended navigation:
$url = 'index1.php?id=' . rawurlencode((string) $id);Also check that the server route actually contains that file and that the id parameter name matches the code reading $_GET.
Rank #4
Check the rendered element and CSS
- Confirm that each anchor has a complete opening tag, a quoted
hrefand a closing tag. - Confirm that the generated id is present and is the id you expect.
- If the source is correct but clicks do nothing, inspect CSS for an element covering the anchor or a rule such as
pointer-events: none.
Use one query or separate menu and content queries?
A single keyed result can work for a small, fixed page set: load the rows, loop over them for the menu, then select the requested row by id. As the site grows, separate queries are easier to maintain.
One combined query
- Convenient when the complete page list is small.
- Allows immediate menu generation and in-memory lookup.
- Consumes more memory as the number or size of pages increases.
Separate queries
- Run a query for the menu fields, such as
idandpageheader. - Read and validate the requested id.
- Run a parameterized content query for that id.
$menu = $pdo->query(
'SELECT id, pageheader FROM pages ORDER BY pageheader'
)->fetchAll();
$id = filter_input(INPUT_GET, 'id', FILTER_VALIDATE_INT);
$contentStmt = $pdo->prepare(
'SELECT pageheader, pagecontent FROM pages WHERE id = :id'
);
$contentStmt->execute(['id' => $id]);
$page = $contentStmt->fetch();This split prevents menu pagination or search from accidentally omitting the page requested in the URL, and it avoids transferring full page content merely to draw navigation.
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Quick Recap
A practical troubleshooting checklist
- Inspect the object returned by the query and establish whether it is PDO or mysqli.
- Use only that API’s methods and constants.
- For PDO associative rows, set
PDO::ATTR_DEFAULT_FETCH_MODEor passPDO::FETCH_ASSOC. - For an id-keyed PDO array, select
idfirst and callfetchAll(PDO::FETCH_UNIQUE). - Validate the requested id before reading the array or displaying content.
- View the browser’s generated source and correct any filename, query-string or malformed-anchor error.
- Inspect CSS only after confirming that the HTML and target URL are correct.
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