Before add to cart, how to get the simple product of configurable product which would be added?

Notice the Before, because I need compare the simple product attribute with products already in cart to decide whether to add it to shopping cart.

In the core CartController - addAction, it has the parent configurable product $product = $this->_initProduct(); and super_attribute in $params['super_attribute'], I guess use both could get the child simple product, but doesn't find a way after many attempts.

Anyone could give a help? Thanks.

2 Answers 2


After a research, finally I found the function getProductByAttributes in app/code/core/Mage/Catalog/Model/Product/Type/Configurable.php, use it could get the child simple product like below.

$childProduct = Mage::getModel('catalog/product_type_configurable')->getProductByAttributes($params['super_attribute'], $product);

The function getProductByAttributes could use a reference when need write similar function, so I will show it here for future reference.

 * Retrieve used product by attribute values
 *  $attrbutesInfo = array(
 *      $attributeId => $attributeValue
 *  )
 * @param  array $attributesInfo
 * @param  Mage_Catalog_Model_Product $product
 * @return Mage_Catalog_Model_Product|null
public function getProductByAttributes($attributesInfo, $product = null)
    if (is_array($attributesInfo) && !empty($attributesInfo)) {
        $productCollection = $this->getUsedProductCollection($product)->addAttributeToSelect('name');
        foreach ($attributesInfo as $attributeId => $attributeValue) {
            $productCollection->addAttributeToFilter($attributeId, $attributeValue);
        $productObject = $productCollection->getFirstItem();
        if ($productObject->getId()) {
            return $productObject;

        foreach ($this->getUsedProducts(null, $product) as $productObject) {
            $checkRes = true;
            foreach ($attributesInfo as $attributeId => $attributeValue) {
                $code = $this->getAttributeById($attributeId, $product)->getAttributeCode();
                if ($productObject->getData($code) != $attributeValue) {
                    $checkRes = false;
            if ($checkRes) {
                return $productObject;
    return null;

Create events.xml at app\code\Vendor\Extension\etc\

<?xml version="1.0"?> 
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
 <event name="checkout_cart_product_add_after">
 <observer name="checkout_cart_after" instance="Vendor\Extension\Observer\Cart\AddtocartbeforeObserver" />

Create AddtocartbeforeObserver.php at app/code/Vendor/Extension/Observer/Cart/

namespace Vendor\Extension\Observer\Cart;

use Magento\ConfigurableProduct\Model\Product\Type\Configurable;
class AddtocartbeforeObserver implements ObserverInterface
    public function __construct(
    Configurable $configurableproduct,
        \Magento\Framework\App\RequestInterface $request
    $this->configurableproduct = $configurableproduct;
        $this->request = $request;

    public function execute(\Magento\Framework\Event\Observer $observer)
        $item = $observer->getEvent()->getData('quote_item');  
         $product = $observer->getEvent()->getData('product');  
        $productData = $this->request->getParams();
    if ($product->getTypeId() == \Magento\ConfigurableProduct\Model\Product\Type\Configurable::TYPE_CODE) 
            $attributes = $productData['super_attribute'];
            $simple_product = $this->configurableproduct->getProductByAttributes($attributes, $product);
           // echo $simple_product->getId();


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