Update a custom field on "Update Cart" click in WooCommerce Cart - php

Question

I added a custom <select> field to each product in cart page to be able to update variation, but when I change it's value and click "Update Cart", nothing updates unless quantity field has also been changed.
Is there a way to avoid this?
My code:
functions.php file:
add_filter( 'woocommerce_update_cart_action_cart_updated', 'on_action_cart_updated', 20, 1 );
function on_action_cart_updated( $cart_updated ){
if ($cart_updated) {
$cart_content = WC()->cart->get_cart_contents();
$update_cart = false;
$cart_totals = isset( $_POST['cart'] ) ? wp_unslash( $_POST['cart'] ) : '';
if ( ! empty( $cart_content ) && is_array( $cart_totals ) ) {
foreach ($cart_content as $key => $item) {
$lease_period = $cart_totals[$key]['lease'];
if ( ! empty( $lease_period )) {
$cart_content[$key]['variation']['attribute_pa_lease-period'] = $lease_period;
$update_cart = true;
}
}
if ($update_cart) {
WC()->cart->set_cart_contents($cart_content);
}
}
}
}
cart.php file:
<td class="product-lease-period" data-title="<?php esc_attr_e( 'Lease Period', 'woocommerce' ); ?>">
<div class="product-lease-period-select">
<select name="cart[<?php echo $cart_item_key ?>][lease]">
<?php
$lease_periods = ['6-months'=> '6 Months',
'12-months' => '12 Months',
'18-months' => '18 Months',
'24-months' => '24 Months'];
foreach ($lease_periods as $key => $period) {
$selected = '';
if ($cart_item['variation']['attribute_pa_lease-period'] == $key) {
$selected = 'selected="selected"';
}
echo "<option value=" . $key . " $selected>" . $period . "</option>";
}
?>
</select>
</div>
</td>
My conclusions so far:
I believe it's because of these pieces of code inside the class-wc-form-handler.php :
// Skip product if no updated quantity was posted.
if ( ! isset( $cart_totals[ $cart_item_key ] ) || ! isset( $cart_totals[ $cart_item_key ]['qty'] ) ) {
continue;
}
and a bit below:
if ( '' === $quantity || $quantity === $values['quantity'] ) {
continue;
}

Answer 1

I extended the WC_Form_Handler class in my functions.php file, copied a method I needed and edited it, and gave it higher hook priority in my extended class than it's in the original class:
class WC_Form_Handler_Ext extends WC_Form_Handler {
/**
* Hook in method.
*/
public static function init() {
add_action( 'wp_loaded', array( __CLASS__, 'update_cart_action' ), 30 );
}
/**
* Remove from cart/update.
*/
public static function update_cart_action() {
// method content edited
}
}
WC_Form_Handler_Ext::init();
UPDATE:
To make price change after variation value in cart is updated, this function needs to be added to the functions.php
function find_matching_product_variation_id($product_id, $attributes)
{
return (new WC_Product_Data_Store_CPT())->find_matching_product_variation(
new WC_Product($product_id),
$attributes
);
}
And it should be called from the loop in functions.php I mentioned in my question this way:
$attributes = $cart_content[$key]['variation'];
$variation_id = find_matching_product_variation_id($product_id, $attributes);
$price = get_post_meta($variation_id, '_price', true);
$item['data']->set_price($price);