I checked with a product with some options. It work. The quantity of the kind of this product decreased after order confirm.
But a product without option, the Total quantity of this product not decreased after order confirm.
Please show me how to setup that feature.
I saw the code in same model file, line 215:
This code checked 'subtract' value in database table 'ac_order_products' to Subtract the quantity in table 'ac_products'.
But I viewed my database, value of field 'subtract' is '0' in table 'ac_order_products', and is '1' in table 'ac_products'.
$order_product_query = $this->db->query("SELECT *
FROM " . DB_PREFIX . "order_products
WHERE order_id = '" . (int)$order_id . "'");
foreach ($order_product_query->rows as $product) {
if ($product['subtract']) {
$this->db->query("UPDATE " . DB_PREFIX . "products
SET quantity = (quantity - " . (int)$product['quantity'] . ")
WHERE product_id = '" . (int)$product['product_id'] . "'");
}