Product compare plugin not working

Question

Here is the plugin i created for limiting 3 products can be added into comparison. But it not loading, add one know what is the problem?

etc/frontend/di.xml

<?xml version="1.0"?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">

    <type name="Magento\Catalog\Controller\Product\Compare\Add">
        <plugin name="LimitToCompareProducts"
                type="Custom\TestCompare\Plugin\LimitToCompareProducts"/>
    </type>
</config>

etc/module.xml

<?xml version="1.0"?>
<!--
/**
 * 
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/Module/etc/module.xsd">
    <module name="Custom_TestCompare" setup_version="1.0.0"/>
</config>

Plugin/LimitToCompareProducts.php

<?php

namespace Custom\TestCompare\Plugin;

    use Magento\Framework\Controller\Result\RedirectFactory;
    use Magento\Framework\Message\ManagerInterface;
    use Magento\Catalog\Helper\Product\Compare;
    
    class LimitToCompareProducts
    {
        const LIMIT_TO_COMPARE_PRODUCTS = 3;
    
        /**
         * @var \Magento\Framework\Message\ManagerInterface
         */
        protected $messageManager;
    
        /**
         * @var RedirectFactory
         */
        protected $resultRedirectFactory;
    
        /** @var Compare */
        protected $helper;
    
        /**
         * RestrictCustomerEmail constructor.
         * @param Compare $helper
         * @param RedirectFactory $redirectFactory
         * @param ManagerInterface $messageManager
         */
        public function __construct(
            RedirectFactory $redirectFactory,
            Compare $helper,
            ManagerInterface $messageManager
        )
        {
            $this->helper = $helper;
            $this->resultRedirectFactory = $redirectFactory;
            $this->messageManager = $messageManager;
        }
    
        public function aroundExecute(
            \Magento\Catalog\Controller\Product\Compare\Add $subject,
            \Closure $proceed
        ){
    
            $count = $this->helper->getItemCount();
            if($count > self::LIMIT_TO_COMPARE_PRODUCTS) {
                $this->messageManager->addErrorMessage(
                    'You can add the compared products under 3 item(s)'
                );
    
                /** @var \Magento\Framework\Controller\Result\Redirect $resultRedirect */
                $resultRedirect = $this->resultRedirectFactory->create();
                return $resultRedirect->setRefererOrBaseUrl();
            }
    
            return $proceed();
        }
    }

registration.php

<?php
\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'Custom_TestCompare',
    __DIR__
);

Answer 1

First thing I would do is add a dependency on Magento_Catalog which should change the load order of the modules so that yours loads after Magento_Catalog:

In etc/module.xml:

<?xml version="1.0"?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Custom_TestCompare" setup_version="1.0.0">
        <sequence>
            <module name="Magento_Catalog"/>
        <sequence>
    </module>
</config>

Then run php bin/magento setup:upgrade so that your module load order changes in app/etc/config.php.

Outside of that, did you do the following?

• Verify that your module is enabled in app/etc/config.php (should see Custom_TestCompare => 1 in the module list)
• Verify the path to the module is app/code/Custom/TestCompare

Compare Limit Logic

Also noticed that you check if $count > 3. Should it be $count >= 3 to prevent a customer from being allowed to add 4 items before your plugin limits?