Magento 2 — Module — Create Plugin

Plugin is a feature that Magento 2 Has to execute something base on it’s function. It can be beforeMethodName, aroundMethodName, and/or afterMethodName. You can read on the official page of it here : https://devdocs.magento.com/guides/v2.3/extension-dev-guide/plugins.html

How to Make it?

1. Create etc/di.xml

Go to etc directory to make this file.

<?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\Adminhtml\Product\Save">
        <plugin name="Icube_Training_AssignSaveProduct" type="Icube\Training\Plugin\AssignSaveProduct" sortOrder="1"/>
    </type>
</config>

Explanation:

• Magento\Catalog\Controller\Adminhtml\Product\Save : Path to the Class that we want to intercept.
• Icube_Training_AssignSaveProduct : Plugin Name.
• Icube\Training\Plugin\AssignSaveProduct : Path to plugin/interceptor Class.

2. Create Plugin/ClassName.php

Inside the directory of Plugin, make that Class with the name Plugin\AssignSaveProduct :

<?php
namespace Icube\Training\Plugin;
use \Magento\Catalog\Controller\Adminhtml\Product\Save;
class AssignSaveProduct
{
    protected $categoryLinkManagement;
public function afterExecute(Save $subject, $result) {
        $data = $subject->getRequest()->getPostValue();
        $training_id = 14;
$categories = $data['product']['category_ids'];
        if (array_search($training_id, $categories) === FALSE) {
            array_push($categories, $training_id);
        }
$this->getCategoryLinkManagement()->assignProductToCategories(
            $data['product']['sku'],
            $categories
        );
return $result;
    }
private function getCategoryLinkManagement()
    {
        if (null === $this->categoryLinkManagement) {
            $this->categoryLinkManagement = \Magento\Framework\App\ObjectManager::getInstance()
                ->get('Magento\Catalog\Api\CategoryLinkManagementInterface');
        }
        return $this->categoryLinkManagement;
    }
}

Don’t forget to execute on command line bin/magento setup:di:compile and bin/magento cache:flush, then run it!