Magento2 how to create a dependent product

Question

Magneto2 How can I create dependent simple products?

First, parent simple product is added to cart & then the second simple product is added to cart.

If first is removed then display an error message.

How can I achieve this functionality?

Answer 1

So assuming a hard coded product parent-child relationship.

The product with sku="product-a" has a child sku="product-b"

• When "product-a" is added to cart we want to add "product-b"
• When "product-a" is removed we display an error message

I used observers for this, hooking into checkout_cart_product_add_after and sales_quote_remove_item.

app/code/StackExchange/DependentProduct/etc/events.xml

<?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="add_dependent_product_to_cart" instance="StackExchange\DependentProduct\Observer\AddDependentProductToCart" />
    </event>
    <event name="sales_quote_remove_item">
        <observer name="remove_dependent_product_from_cart" instance="StackExchange\DependentProduct\Observer\RemoveDependentProductFromCart" />
    </event>
</config>

app/code/StackExchange/DependentProduct/Observer/AddDependentProductToCart.php

<?php
declare(strict_types=1);

namespace StackExchange\DependentProduct\Observer;

use Magento\Catalog\Model\ProductRepository;
use Magento\Checkout\Model\Session;
use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;
use Magento\Quote\Api\CartRepositoryInterface;
use Magento\Quote\Model\Quote;

class AddDependentProductToCart implements ObserverInterface
{
    /**
     * @var ProductRepository
     */
    private ProductRepository $productRepository;
    /**
     * @var CartRepositoryInterface
     */
    private CartRepositoryInterface $cartRepository;
    /**
     * @var Session
     */
    private Session $checkoutSession;

    public function __construct(
        Session $checkoutSession,
        ProductRepository $productRepository,
        CartRepositoryInterface $cartRepository
    ) {
        $this->productRepository = $productRepository;
        $this->cartRepository = $cartRepository;
        $this->checkoutSession = $checkoutSession;
    }

    public function execute(Observer $observer)
    {
        /** @var \Magento\Catalog\Model\Product $product */
        $product = $observer->getEvent()->getData('product');

        if ($product->getSku() != "product-a") {
            return;
        }
        /** @var \Magento\Quote\Model\Quote\Item $quoteItem */
        $quoteItem = $observer->getEvent()->getData('quote_item');
        $productB = $this->productRepository->get('product-b');

        $quote = $this->checkoutSession->getQuote();

        $quote->addProduct($productB, (int) $quoteItem->getQty());
    }
}

app/code/StackExchange/DependentProduct/Observer/RemoveDependentProductFromCart.php

<?php
declare(strict_types=1);

namespace StackExchange\DependentProduct\Observer;

use Magento\Catalog\Model\ProductRepository;
use Magento\Checkout\Model\Session;
use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\Message\ManagerInterface as MessageManager;
use Magento\Quote\Api\CartRepositoryInterface;

class RemoveDependentProductFromCart implements ObserverInterface
{
    private MessageManager $messageManager;

    public function __construct(
        MessageManager $messageManager
    ) {
        $this->messageManager = $messageManager;
    }

    public function execute(Observer $observer)
    {
        /** @var \Magento\Quote\Model\Quote\Item $quoteItem */
        $quoteItem = $observer->getEvent()->getData('quote_item');

        if ($quoteItem->getSku() != "product-a") {
            return;
        }

        $this->messageManager->addErrorMessage(__('Error message'));
    }

}

You might need to review so that the correct qty are added to cart if a product is added several times. There is also another event checkout_cart_product_update_after you might want to look into. However, the above code shows the basic idea.

Good luck!