EAV and extension attributes

There are two types of attributes you can use to extend Magento functionality:

• Custom and Entity-Attribute-Value (EAV) attributes—Custom attributes are those added on behalf of a merchant. For example, a merchant might need to add attributes to describe products, such as shape or volume. A merchant can add these attributes on the admin panel. See the merchant documentation for information about managing custom attributes.

  Custom attributes are a subset of EAV attributes. Objects that use EAV attributes typically store values in several MySQL tables. The Customer and Catalog modules are the primary models that use EAV attributes. Other modules, such as ConfigurableProduct, GiftMessage, and Tax, use the EAV functionality for Catalog.

• Extension attributes. Extension attributes are new in Magento 2. They are used to extend functionality and often use more complex data types than custom attributes. These attributes do not appear in the MAgento Admin.

EAV and custom attributes

CustomAttributesDataInterface defines the methods that are called to get and set custom attributes, including getCustomAttributes().

A module has a set of built-in attributes that are always available. The Catalog module has several attributes that are defined as EAV attributes, but are treated as built-in attributes. These attributes include:

• attribute_set_id
• created_at
• group_price
• media_gallery
• name
• price
• sku
• status
• store_id
• tier_price
• type_id
• updated_at
• visibility
• weight

In this case, when getCustomAttributes() is called, the system returns only custom attributes that are not in this list.

The Customer module does not treat its EAV attributes in a special manner. As a result, the getCustomAttributes() method returns all EAV attributes.

Adding Customer EAV attribute for backend only

Customer attributes are created inside of InstallData and UpgradeData scripts. To add new attributes to the database, you must use the \Magento\Eav\Setup\EavSetup class as a dependency injection.

namespace My\Module\Setup;

use Magento\Customer\Model\Customer;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\ModuleDataSetupInterface;

class InstallData implements \Magento\Framework\Setup\InstallDataInterface
{
    private $eavSetup;
    
    private $eavConfig;
    
    private $attributeResource;
    
    public function __construct(
        \Magento\Eav\Setup\EavSetup $eavSetup,
        \Magento\Eav\Model\Config $eavConfig,
        \Magento\Customer\Model\ResourceModel\Attribute $attributeResource
    ) {
        $this->eavSetup = $eavSetup;
        $this->eavConfig = $eavConfig;
        $this->attributeResource = $attributeResource;
    }
    
    public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
    {
        $this->eavSetup->addAttribute(Customer::ENTITY, 'attribute_code', [
            // Attribute parameters
        ]);
        
        $attribute = $this->eavConfig->getAttribute(Customer::ENTITY, 'attribute_code');
        $attribute->setData('used_in_forms', ['adminhtml_customer']);
        $this->attributeResource->save($attribute);
    }
}

Extension attributes

Use ExtensibleDataInterface to implement extension attributes. In your code, you must define getExtensionAttributes() and setExtensionAttributes(*ExtensionInterface param).

public function getExtensionAttributes();

Most likely, you will want to extend interfaces defined in the Api/Data directory of a Magento module.

Declare extension attributes

You must create a <Module>/etc/extension_attributes.xml file to define a module’s extension attributes:

<config>
    <extension_attributes for="Path\To\Interface">
        <attribute code="name_of_attribute" type="datatype">
           <resources>
              <resource ref="permission"/>
           </resources>
           <join reference_table="" reference_field="" join_on_field="">
              <field>fieldname</field>
           </join>
        </attribute>
    </extension_attributes>
</config>

where:

Searching extension attributes

The system uses a join directive to add external attributes to a collection and to make the collection filterable. The join element in the extension_attributes.xml file defines which object fields and the database table/column to use as the source of a search.

In the following example, an attribute named stock_item of type Magento\CatalogInventory\Api\Data\StockItemInterface is being added to the Magento\Catalog\Api\Data\ProductInterface.

<extension_attributes for="Magento\Catalog\Api\Data\ProductInterface">
    <attribute code="stock_item" type="Magento\CatalogInventory\Api\Data\StockItemInterface">
        <join reference_table="cataloginventory_stock_item" reference_field="product_id" join_on_field="entity_id">
            <field>qty</field>
        </join>
    </attribute>
</extension_attributes>

When getList() is called, it returns a list of ProductInterfaces. When it does this, the code populates the stock_item with a joined operation in which the StockItemInterface’s qty property comes from the cataloginventory_stock_item table where the Product’s entity_Id is joined with the cataloginventory_stock_item.product_id column.

Extension attribute authentication

Individual fields that are defined as extension attributes can be restricted, based on existing permissions. This feature allows extension developers to restrict access to data. See Web API authentication overview for general information about authentication in Magento.

The following code sample defines stock_item as an extension attribute of the CatalogInventory module. CatalogInventory is treated as a “third-party extension”. Access to the inventory data is restricted because the quantity of in-stock item may be competitive information.

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Api/etc/extension_attributes.xsd">
    <extension_attributes for="Magento\Catalog\Api\Data\ProductInterface">
        <attribute code="stock_item" type="Magento\CatalogInventory\Api\Data\StockItemInterface">
            <resources>
                <resource ref="Magento_CatalogInventory::cataloginventory"/>
            </resources>
        </attribute>
    </extension_attributes>
</config>

In this example, the stock_item attribute is restricted to only the users who have the Magento_CatalogInventory::cataloginventory permission. As a result, an anonymous or unauthenticated user issuing a GET http://<magento_base_url>/rest/V1/products/<sku> request will receive product information similar to the following:

{
  "sku": "tshirt1",
  "price": "20.00",
  "description": "New JSmith design",
  "extension_attributes": {
    "logo size": "small"
  },
  "custom_attributes": {
    "artist": "James Smith"
  }
}

However, an authenticated user with the permission Magento_CatalogInventory::cataloginventory receives the additional stock_item field:

{
  "sku": "tshirt1",
  "price": "20.00",
  "description": "New JSmith design",
  "extension_attributes": {
    "logo size": "small",
    "stock_item" : {
      "status" : "in_stock"
      "quantity": 70
    }
  },
  "custom_attributes": {
    "artist": "James Smith"
  }
}

This only works for extension attributes (those attributes defined in an extension_attributes.xml file). There are no permission restrictions on the rest of the returned data. For example, there is no way to restrict custom_attributes.

Extension interfaces

An ExtensionInterface will be empty if no extension attributes have been added. In the following example—in an unmodified installation—CustomerExtensionInterface will be generated, but will be empty:

interface CustomerExtensionInterface extends \Magento\Framework\Api\ExtensionAttributesInterface { }

However, if an extension similar to the following has been defined, the interface will not be empty:

<extension_attributes for="Magento\Customer\Api\Data\CustomerInterface">
    <attribute code="attributeName" type="Magento\Some\Type[]" />
</extension_attributes>

Troubleshoot EAV attributes

If you have issues when using setup:upgrade, verify __construct uses the method EavSetupFactory not EavSetup. You should not directly inject EavSetup in extension code. Check your custom code and purchased modules and extensions to verify. After changing the methods, you should be able to properly deploy.