Limit Add to Cart Items

Question

I want to Limit Checkout Order or Add to Cart Limit to allow only 6 types of products/items. These 6 items can have variable Qty value. Eg: One Checkout/AddCart Maximum 6 Items: Item-1 25Qty, Item-2 125Qty, Item-3 Sample, Item-4 50Qty, Item-5 100Qty, Item-6 Sample,

So for I have created an extension using Event Observer but it is not working.

code of Vendor/Module/etc/events.xml

<?xml version="1.0" encoding="UTF-8"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="controller_action_predispatch_checkout_cart_add">
        <observer name="limit_items_in_cart_checkout_before" instance="Vendor\Module\Observer\Checkout\Cart\Add" />
    </event>
</config>

code of Vendor/Module/Observer/Checkout/Cart/Add.php

<?php

namespace Vendor\Module\Observer\Checkout\Cart;

use Magento\Checkout\Model\Session;
use Magento\Framework\App\ActionFlag;
use Magento\Framework\App\Response\RedirectInterface as ResponseRedirect;
use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\Message\ManagerInterface as MessageManager;

class Add implements ObserverInterface
{
    /** @var Session $session */
    private $session;

    /** @var ActionFlag $flag */
    private $flag;

    /** @var ResponseRedirect $redirect */
    private $redirect;

    /** @var MessageManager $messageManager */
    private $messageManager;

    /**
     * Add constructor.
     *
     * @param Session          $session
     * @param ActionFlag       $flag
     * @param ResponseRedirect $redirect
     * @param MessageManager   $messageManager
     */
    public function __construct(
        Session $session,
        ActionFlag $flag,
        ResponseRedirect $redirect,
        MessageManager $messageManager
    ) {
        $this->session         = $session;
        $this->flag            = $flag;
        $this->redirect        = $redirect;
        $this->messageManager  = $messageManager;
    }

    /**
     * @param Observer $observer
     *
     * @return $this|void
     * @throws \Magento\Framework\Exception\LocalizedException
     * @throws \Magento\Framework\Exception\NoSuchEntityException
     */
    public function execute(Observer $observer)
    {
        $quote      = $this->session->getQuote();
        $itemsCount = $quote->getItemsCount();

        if ($itemsCount > 6) {
            $request = $observer->getRequest();
            $request->setParams([
                'product'    => false,
                'return_url' => $this->redirect->getRefererUrl(),
                'backUrl'    => $this->redirect->getRefererUrl()
            ]);

            $this->messageManager->addErrorMessage(
                __('Only 6 types of products per purchase allowed. Please complete this order first and place another order afterwards.')
            );

            $action = $observer->getEvent()->getControllerAction();
            $this->flag->set('', \Magento\Framework\App\ActionInterface::FLAG_NO_DISPATCH, true);
            $action->getResponse()->setRedirect('/checkout/cart');

            return $this;
        }
    }
}

Answer 1

Just update the code for your Observer Vendor/Module/Observer/Checkout/Cart/Add.php

<?php

namespace Vendor\Module\Observer\Checkout\Cart;

use Magento\Checkout\Model\Session;
use Magento\Framework\App\ActionFlag;
use Magento\Framework\App\Response\RedirectInterface as ResponseRedirect;
use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\Message\ManagerInterface as MessageManager;

class Add implements ObserverInterface
{
    /** @var Session $session */
    private $session;

    /** @var ActionFlag $flag */
    private $flag;

    /** @var ResponseRedirect $redirect */
    private $redirect;

    /** @var MessageManager $messageManager */
    private $messageManager;

    /**
     * Add constructor.
     *
     * @param Session          $session
     * @param ActionFlag       $flag
     * @param ResponseRedirect $redirect
     * @param MessageManager   $messageManager
     */
    public function __construct(
        \Magento\Framework\App\RequestInterface $request,
        \Magento\Checkout\Model\Cart $cart,
        ResponseRedirect $redirect,
        MessageManager $messageManager
    ) {
        $this->_request        = $request;
        $this->_cart           = $cart;
        $this->redirect        = $redirect;
        $this->messageManager  = $messageManager;
    }

    /**
     * @param Observer $observer
     *
     * @return $this|void
     * @throws \Magento\Framework\Exception\LocalizedException
     * @throws \Magento\Framework\Exception\NoSuchEntityException
     */
    public function execute(Observer $observer)
    {
        $controller = $observer->getControllerAction();
        $postValues = $this->_request->getPostValue();
        $cartQuote = $this->_cart->getQuote()->getData();
        $cartItemsCount = $this->_cart->getQuote()->getItemsCount();
        $cartItemsAll = $this->_cart->getQuote()->getAllItems();
 
        if($cartItemsCount > 5)
        {
            $observer->getRequest()->setParam('product', false);
            $observer->getRequest()->setParam('return_url', $this->redirect->getRefererUrl());
            $observer->getRequest()->setParam('backUrl', $this->redirect->getRefererUrl());
            $this->messageManager->addErrorMessage(
                __('Only 6 types of products per purchase allowed. Please complete this order first and place another order afterwards.')
            );
        }
    }
}

Hope this helps!