PHP购物车实施

Question

我正在尝试为我的基础学习php项目实现购物车。我正在使用这个：Running Example工具来简化它。该工具需要一个json工作，我很难从数据库中获取我的自定义产品，并尝试将它们编码为json。这就是我目前所拥有的：

<?php
// A collection of sample products
require_once "connect.php";
$return_arr = array();

$query = "SELECT * FROM products";

$stmt = $pdo->prepare($query);

$stmt->execute();

while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    $row_array['id'] = $row['id'];
    $row_array['name'] = $row['name'];
    $row_array['description'] = $row['description'];
    $row_array['price'] = $row['price'];
    $row_array['picture'] = $row['picture'];
    $row_array['quantity'] = $row['quantity'];
    array_push($return_arr,$row_array);
}

json_encode($return_arr);
echo "<div>$return_arr</div>";
$products = json_decode("{$return_arr}", true);


// Page
$a = (isset($_GET['a'])) ? $_GET['a'] : 'home';

require_once 'class.Cart.php';

// Initialize cart object
$cart = new Cart([
    // Maximum item can added to cart, 0 = Unlimited
    'cartMaxItem' => 0,

    // Maximum quantity of a item can be added to cart, 0 = Unlimited
    'itemMaxQuantity' => 5,

    // Do not use cookie, cart items will gone after browser closed
    'useCookie' => false,
]);

// Shopping Cart Page
if ('cart' == $a) {
    $cartContents = '
    <div class="alert alert-warning">
        <i class="fa fa-info-circle"></i> There are no items in the cart.
    </div>';

    // Empty the cart
    if (isset($_POST['empty'])) {
        $cart->clear();
    }

    // Add item
    if (isset($_POST['add'])) {
        foreach ($products as $product) {
            if ($_POST['id'] == $product->id) {
                break;
            }
        }

        $cart->add($product->id, $_POST['qty'], [
            'price' => $product->price,
            'color' => (isset($_POST['color'])) ? $_POST['color'] : '',
        ]);
    }

    // Update item
    if (isset($_POST['update'])) {
        foreach ($products as $product) {
            if ($_POST['id'] == $product->id) {
                break;
            }
        }

        $cart->update($product->id, $_POST['qty'], [
            'price' => $product->price,
            'color' => (isset($_POST['color'])) ? $_POST['color'] : '',
        ]);
    }

    // Remove item
    if (isset($_POST['remove'])) {
        foreach ($products as $product) {
            if ($_POST['id'] == $product->id) {
                break;
            }
        }

        $cart->remove($product->id, [
            'price' => $product->price,
            'color' => (isset($_POST['color'])) ? $_POST['color'] : '',
        ]);
    }

    if (!$cart->isEmpty()) {
        $allItems = $cart->getItems();

        $cartContents = '
        <table class="table table-striped table-hover">
            <thead>
                <tr>
                    <th class="col-md-7">Product</th>
                    <th class="col-md-3 text-center">Quantity</th>
                    <th class="col-md-2 text-right">Price</th>
                </tr>
            </thead>
            <tbody>';

        foreach ($allItems as $id => $items) {
            foreach ($items as $item) {
                foreach ($products as $product) {
                    if ($id == $product->id) {
                        break;
                    }
                }

                $cartContents .= '
                <tr>
                    <td>'.$product->name.((isset($item['attributes']['color'])) ? ('<p><strong>Color: </strong>'.$colors[$item['attributes']['color']].'</p>') : '').'</td>
                    <td class="text-center"><div class="form-group"><input type="number" value="'.$item['quantity'].'" class="form-control quantity pull-left" style="width:100px"><div class="pull-right"><button class="btn btn-default btn-update" data-id="'.$id.'" data-color="'.((isset($item['attributes']['color'])) ? $item['attributes']['color'] : '').'"><i class="fa fa-refresh"></i> Update</button><button class="btn btn-danger btn-remove" data-id="'.$id.'" data-color="'.((isset($item['attributes']['color'])) ? $item['attributes']['color'] : '').'"><i class="fa fa-trash"></i></button></div></div></td>
                    <td class="text-right">$'.$item['attributes']['price'].'</td>
                </tr>';
            }
        }

        $cartContents .= '
            </tbody>
        </table>

        <div class="text-right">
            <h3>Total:<br />$'.number_format($cart->getAttributeTotal('price'), 2, '.', ',').'</h3>
        </div>

        <p>
            <div class="pull-left">
                <button class="btn btn-danger btn-empty-cart">Empty Cart</button>
            </div>
            <div class="pull-right text-right">
                <a href="?a=home" class="btn btn-default">Continue Shopping</a>
                <a href="#" class="btn btn-danger">Checkout</a>
            </div>
        </p>';
    }
}
?>

当我运行代码时，它会给出错误：“在第23行的C：\ xampp \ htdocs \ BeerShop2 \ basket.php中进行字符串转换”。我试图弄清楚出了什么问题，似乎问题在于解码。如何从数据库中获取所有产品的查询，然后使用该工具解码json？