PostgreSQL INSERT语句在PHP中与PDO不兼容

This one is leaving me scratching my head. I'm sure I'm missing something simple, but for the life of me I can't see what when I compare it to other INSERT statements I've written that work just fine. The parameters are being passed when I check the network tab in developer, but it won't forward to the page specified in the header, and the table is not updated with information when I fill in the form.

Here is the function I wrote in the model layer:

function add_yarn($yarnbrand, $yarnamount, $yarnweight, $yarncolor) {
global $db;
$query = 'INSERT INTO yarn
             (yarnbrand, yarnamount, yarnweight, yarncolor)
          VALUES
             (:yarnbrand, :yarnamount, :yarnweight, :yarncolor)';

$statement = $db->prepare($query);
$statement->bindValue(':yarnbrand', $yarnbrand);
$statement->bindValue(':yarnamount', $yarnamount);
$statement->bindValue(':yarnweight', $yarnweight);
$statement->bindValue(':yarncolor', $yarncolor);
$statement->execute();
$statement->closeCursor();
}

Here is the control layer in for the action associated with that function in index.php:

case 'yarn_add' :
    $yarnbrand = filter_input(INPUT_POST, 'yarnbrand');
    $yarnamount = filter_input(INPUT_POST, 'yarnamount', FILTER_VALIDATE_INT);
    $yarnweight = filter_input(INPUT_POST, 'yarnweight');
    $yarncolor = filter_input(INPUT_POST, 'yarncolor');

    if ($yarnbrand == NULL || $yarnamount == NULL ||
            $yarnweight == NULL || $yarncolor == NULL) {
        echo 'Empty or invalid data input.';
    } else { 
        add_yarn($yarnbrand, $yarnamount, $yarnweight, $yarncolor);
        header('Location: index.php?action=view_yarn');
    }
    break;

and here is the view layer with the add form:

<?php include '../view/header.php'; ?>

<main>
<h1>Add Yarn</h1>
    <form action="index.php" method="post" id="add_yarn_form">
        <input type="hidden" name="action" value="yarn_add">

        <label>Brand:</label>
        <input type="text" name="yarnbrand"> <br>

        <label>Weight:</label>
        <input type="text" name="yarnweight"><br>

        <label>Amount:</label>
        <input type="text" name="yarnamount"><br>

        <label>Color:</label>
        <input type="text" name="yarncolor"><br>

        <label>&nbsp;</label>
        <input type="submit" value="Save Changes"><br>
    </form>
<div class="bottomtext">
    <a href="index.php?action=view_yarn">View Yarns</a>
    <a href="index.php?action=list_supplies">View Supplies</a>
</div>

</main>
<?php include '../view/footer.php'; ?>

I appreciate any help!

Maybe a variable with an illegal caracter ? You don't use filters in your filter_input, expected for the integer variable.

Take a look on the manual :

If omitted, FILTER_DEFAULT will be used, which is equivalent to FILTER_UNSAFE_RAW. This will result in no filtering taking place by default.

Not really secure :/