Using fetch_assoc on prepared statements

I'm currently working on a login script, and I got this code:

$selectUser = $db->prepare("SELECT `id`,`password`,`salt` FROM `users` WHERE `username`=?");
$selectUser->bind_param('s', $username);
$selectUser->execute();

if ($selectUser->num_rows() < 0)
    echo "no_user";
else
{
    $user = $selectUser->fetch_assoc();
    echo $user['id'];
}

Here's the error I get:

Fatal error: Uncaught Error: Call to undefined method mysqli_stmt::fetch_assoc()

I tried all sorts of variations, like:

$result = $selectUser->execute();
$user = $result->fetch_assoc();

and more... nothing worked.

Solution 1:

That's because fetch_assoc is not part of a mysqli_stmt object. fetch_assoc belongs to the mysqli_result class. You can use mysqli_stmt::get_result to first get a result object and then call fetch_assoc:

$selectUser = $db->prepare("SELECT `id`,`password`,`salt` FROM `users` WHERE `username`=?");
$selectUser->bind_param('s', $username);
$selectUser->execute();
$result = $selectUser->get_result();
$assoc = $result->fetch_assoc();

Alternatively, you can use bind_result to bind the query's columns to variables and use fetch() instead:

$selectUser = $db->prepare("SELECT `id`,`password`,`salt` FROM `users` WHERE `username`=?");
$selectUser->bind_param('s', $username);
$selectUser->bind_result($id, $password, $salt);
$selectUser->execute();
while($selectUser->fetch())
{
    //$id, $password and $salt contain the values you're looking for
}