One of the most popular operations that we will need on Magento, is adding a custom attribute to our catalog products. To do so, basically, we will need to perform the following steps:

1. Create a new module
2. Create an InstallData script
   • app/code/Offset101/ProductAttributeExample/Setup/InstallData.php:
     
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     <?php   namespace Offset101\ProductAttributeExample\Setup;   use Magento\Framework\Setup\InstallDataInterface; use Magento\Framework\Setup\ModuleContextInterface; use Magento\Framework\Setup\ModuleDataSetupInterface;   /** * Class InstallData * @package Offset101\ProductAttributeExample\Setup */ class InstallData implements InstallDataInterface {     /**      * @var \Magento\Eav\Setup\EavSetupFactory      */     private $eavSetupFactory;       /**      * InstallData constructor.      * @param \Magento\Eav\Setup\EavSetupFactory $eavSetupFactory      */     public function __construct(\Magento\Eav\Setup\EavSetupFactory $eavSetupFactory)     {         $this->eavSetupFactory = $eavSetupFactory;     }         public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)     {         $eavSetup = $this->eavSetupFactory->create(['setup' => $setup]);         $eavSetup->addAttribute(             \Magento\Catalog\Model\Product::ENTITY,             'canonical_path_url',             [                 'type' => 'text',                 'backend' => '',                 'frontend' => '',                 'label' => 'Canonical Path URL',                 'input' => 'text',                 'class' => '',                 'global' => \Magento\Eav\Model\Entity\Attribute\ScopedAttributeInterface::SCOPE_GLOBAL,                 'visible' => true,                 'required' => false,                 'user_defined' => false,                 'default' => '',                 'searchable' => false,                 'filterable' => false,                 'comparable' => false,                 'visible_on_front' => false,                 'used_in_product_listing' => true,                 'unique' => false,                 'apply_to' => ''             ]         );     } }

   • We can optionally add the following:
     • ‘source’ : A Source model to provide a list of options. We will need to write the method “getAllOptions”.
     • ‘backend’: A backend model to allow you to perform certain actions when an attribute is loaded or saved. ie: a validation. We will need to write the method validate(Object).
     • ‘frontend’: A frontend model to define how it should be rendered on the frontend. We will need to write method getValue(Object).
3. Execute the InstallData script and verify that it works
   
   1 2	cd <magento2_root> php bin/magento setup:upgrade

   • After running this, the new attribute should have been added to the database. You can check the eav_attribute and catalog_eav_attribute tables to verify that the attribute and its properties are there.
   • If the attribute is there, but you need to change something, or re-run your script, you can easily remove the row of your script (or downgrade the version) on the setup_module table.

For more information, you can follow up the following link: How to Add a New Product Attribute