In this article, we will find out how to create a product attribute in Magento 2 programatically. As you know, Magento 2 manage Product by EAV model, so we cannot simply add an attribute for product by adding a column for product table.

Today  I am going to explain, how we can create text & drop down attribute for Products in Magento 2.
There are two ways to create the drop down attribute in Magento.
1 -> Manually : Go To admin panel,  Store -> Attributes -> Product .
2 -> Programmatically .

Overview of Adding Product Attribute Programmatically

Create file InstallData.php

We will start with the InstallData class which located in app/code/Thecoachsmb/ProductAttribute/Setup/InstallData.php. The content for this file:

1. Create Text custom attribute

Here are all lines code of InstallSchema.php to create product attribute programmically.

<?php
namespace Thecoachsmb\ProductAttribute\Setup;

use Magento\Eav\Setup\EavSetup;
use Magento\Eav\Setup\EavSetupFactory;
use Magento\Framework\Setup\InstallDataInterface;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\ModuleDataSetupInterface;

class InstallData implements InstallDataInterface
{
	private $eavSetupFactory;

	public function __construct(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,
			'sample_attribute',
			[
				'type' => 'text',
				'backend' => '',
				'frontend' => '',
				'label' => 'Sample Atrribute',
				'input' => 'text',
				'class' => '',
				'source' => '',
				'global' => \Magento\Eav\Model\Entity\Attribute\ScopedAttributeInterface::SCOPE_GLOBAL,
				'visible' => true,
				'required' => true,
				'user_defined' => false,
				'default' => '',
				'searchable' => false,
				'filterable' => false,
				'comparable' => false,
				'visible_on_front' => false,
				'used_in_product_listing' => true,
				'unique' => false,
				'apply_to' => ''
			]
		);
	}
}

As you can see, all the addAttribute method requires is:

• The type id of the entity which we want to add attribute
• The name of the attribute
• An array of key value pairs to define the attribute such as group, input type, source, label…

All done, please run the upgrade script php bin/magento setup:upgrade to install the module and the product attribute sample_attribute will be created.

After run upgrade complete, please run php bin/magento setup:static-content:deploy and go to product from admin to check the result.

2. Create Dropdown custom attribute

Today  I am going to explain, how we can create drop down attribute for Products in Magento 2.
There are two ways to create the drop down attribute in Magento.
1 -> Manually : Go To admin panel,  Store -> Attributes -> Product .
2 -> Programmatically .

In this blog I am covering how we can create the drop down attribute programmatically,
So let’s start :
Step 1 : create InstallData.php file : Thecoachsmb\ProductAttribute\Setup\InstallData.php
Now In this file, create an Array of the attributes that you want to add as below.

$attributeGroup = 'Test Group';
        $attributes = [
            'attribute_code' => [
                'group'              => $attributeGroup,
                'input'              => 'select',
                'type'               => 'int',
                'label'              => 'Attribute Label',
                'visible'            => true,
                'required'           => false,
                'user_defined'               => true,
                'searchable'                 => false,
                'filterable'                 => false,
                'comparable'                 => false,
                'visible_on_front'           => false,
                'visible_in_advanced_search' => false,
                'is_html_allowed_on_front'   => false,
                'used_for_promo_rules'       => true,
                'source'                     => 'Thecoachsmb\ProductAttribute\Model\Config\Source\Options',
                'frontend_class'             => '',
                'global'                     =>  \Magento\Eav\Model\Entity\Attribute\ScopedAttributeInterface::SCOPE_GLOBAL,
                'unique'                     => false,
                'apply_to'                   => 'simple,grouped,configurable,downloadable,virtual,bundle'
            ],...
          ];

Step 2 : Now Add and Assign Attribute to Group and Attribute Set.

// Add Attribute
// Magento\Eav\Setup\EavSetupFactory  $this->eavSetupFactory
// Magento\Framework\Setup\ModuleDataSetupInterface $setup

 $eavSetup = $this->eavSetupFactory->create(['setup' => $setup]);
            foreach ($attributes as $attribute_code => $attributeOptions) {
                $eavSetup->addAttribute(
                    \Magento\Catalog\Model\Product::ENTITY,
                    $attribute_code,
                    $attributeOptions
                );
            }
//Assign 
            foreach ($attributes as $attribute_code => $attributeOptions) {

                // Class \Magento\Eav\Model\AttributeManagement

                $this->attributeManagement->assign(
                    'catalog_product',
                    $attributeSet->getId(),
                    $groupId,
                    $attribute_code,
                    $attributeSet->getCollection()->getSize() * 10
                );
            }

Note :
$attributeSet : you can load the attribute collection and loop for it or Can pass specific id instead.
$groupId : Magento\Eav\Model\Entity\Attribute\Group : you can get the group id with the help of this class.

Now , Options for drop down attribute , you can add options directly as a array.
and another approach is to use class Magento\Eav\Model\Entity\Attribute\Source\AbstractSource  as follows :

<?php

namespace Thecoachsmb\ProductAttribute\Model\Config\Source;

class Options extends \Magento\Eav\Model\Entity\Attribute\Source\AbstractSource
{
    /**
    * Get all options
    *
    * @return array
    */
    public function getAllOptions()
    {
        $this->_options = [
                ['label' => __('No'), 'value'=>'0'],
                ['label' => __('Yes'), 'value'=>'1'],
                ['label' => __('Other'), 'value'=>'2']
            ];

    return $this->_options;

    }

}

Please read each line carefully, so that you can create the attributes easily.