Adding extension attributes to entity

Third party developers cannot change API Data interface in the Magento Core, so the one way to affect interfaces using configuration is to add extension attributes.

We will demonstrate this on Product entity, Product Repository and Web Api example.

In order to get product or list of products by Magento API you need to do API request to appropriate service (Product Repository in our case). In Response we got object with next structure:

Product response:

<product>
    <id>1</id>
    <sku>some-sku</sku>
    <custom_attributes><!-- Custom Attributes Data --></custom_attributes>
    <extension_attributes><!-- Here should we add extension attributes data --></extension_attributes>
</product>

Product list response:

<products>
    <item>
        <id>1</id>
        <sku>some-sku</sku>
        <custom_attributes><!-- Custom Attributes Data --></custom_attributes>
        <extension_attributes><!-- Here should we add extension attributes data --></extension_attributes>
    </item>
    <item>
        <id>2</id>
        <sku>some-sku-2</sku>
        <custom_attributes><!-- Custom Attributes Data --></custom_attributes>
        <extension_attributes><!-- Here should we add extension attributes data --></extension_attributes>
    </item>
</products>

Add plugin to product repository

In order to add attributes, we need to use after plugin on Product Repository. Plugin should listen next methods: save, get, getList.

We can add scalar and non-scalar extension attributes.

Scalar is simple attribute.

Non-scalar attribute can be represented by Data Object.

public function afterGet
(
    \Magento\Catalog\Api\ProductRepositoryInterface $subject,
    \Magento\Catalog\Api\Data\ProductInterface $entity
) {
    $ourCustomData = $this->customDataRepository->get($entity->getId());

    $extensionAttributes = $entity->getExtensionAttributes(); /** get current extension attributes from entity **/
    $extensionAttributes->setOurCustomData($ourCustomData);
    $entity->setExtensionAttributes($extensionAttributes);

    return $entity;
}

It is the easiest way to add custom attributes. Because we need to know if entity already has extension attributes. Also we need to check whether we already has our extension attribute.

AfterGetList is similar to afterGet.

Likewise afterSave plugin should take data from entity and do some manipulations:

public function afterSave
(
    \Magento\Catalog\Api\ProductRepositoryInterface $subject,
    \Magento\Catalog\Api\Data\ProductInterface $entity
) {
    $extensionAttributes = $entity->getExtensionAttributes(); /** get current extension attributes from entity **/
    $ourCustomData = $extensionAttributes->getOurCustomData();
    $this->customDataRepository->save($ourCustomData);

    return $entity;
}

But if some entity doesn’t have implementation to fetch extension attributes, we will always retrieve null and each time when we fetch extension atrributes we need to check if they are null - need to create them. To avoid such code duplication, we need to create afterGet plugin for our entity with extension attributes.

Let’s assume the product entity doesn’t have any implementation of extension attributes, so our plugin might looks like this:

use Magento\Catalog\Api\Data\ProductExtensionInterface;
use Magento\Catalog\Api\Data\ProductInterface;
use Magento\Catalog\Api\Data\ProductExtensionFactory;

class ProductAttributesLoad
{
    /**
     * @var ProductExtensionFactory
     */
    private $extensionFactory;

    /**
     * @param ProductExtensionFactory $extensionFactory
     */
    public function __construct(ProductExtensionFactory $extensionFactory)
    {
        $this->extensionFactory = $extensionFactory;
    }

    /**
     * Loads product entity extension attributes
     *
     * @param ProductInterface $entity
     * @param ProductExtensionInterface|null $extension
     * @return ProductExtensionInterface
     */
    public function afterGetExtensionAttributes(
        ProductInterface $entity,
        ProductExtensionInterface $extension = null
    ) {
        if ($extension === null) {
            $extension = $this->extensionFactory->create();
        }

        return $extension;
    }
}

And now need to bind our plugin to ProductInterface:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Catalog\Api\Data\ProductInterface">
        <plugin name="ProductExtensionAttributeOperations" type="Magento\Catalog\Plugin\ProductAttributesLoad"/>
    </type>
</config>

Extension Attributes Configuration:

For scalar attributes we can use next configuration:

<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="first_custom_attribute" type="Magento\SomeModule\Api\Data\CustomDataInterface" />
        <attribute code="second_custom_attribute" type="Magento\SomeModule\Api\Data\CustomDataInterface" />
    </extension_attributes>
</config>

For non-scalar attributes:

<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="our_custom_data" type="Magento\SomeModule\Api\Data\CustomDataInterface[]" />
    </extension_attributes>
</config>

In first case we will get the next result:

<product>
    <id>1</id>
    <sku>some-sku</sku>
    <custom_attributes><!-- Custom Attributes Data --></custom_attributes>
    <extension_attributes>
        <first_custom_attribute>1</first_custom_attribute>
        <second_custom_attribute>2</second_custom_attribute>
    </extension_attributes>
</product>

In second one:

<product>
    <id>1</id>
    <sku>some-sku</sku>
    <custom_attributes><!-- Custom Attributes Data --></custom_attributes>
    <extension_attributes>
        <our_custom_data>
                <first_custom_attribute>1</first_custom_attribute>
                <second_custom_attribute>2</second_custom_attribute>
        </our_custom_data>
    </extension_attributes>
</product>

Sample module on github

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