Adding extension attributes to entity

Third-party developers cannot change the API Data interfaces defined in the Magento Core code. However, most of these entities have a feature called extension attributes. Check the interface for the methods getExtensionAttributes() and setExtensionAttributes() to determine if they are available for the entity.

We will demonstrate how to add extension attributes to a Product entity, Product Repository and Web Api example.

In order to retrieve a product or a list of products from the Magento API, you need to make an API request to the appropriate service (the Product Repository in this case). The response to these requests will return objects with the following structure:

Product response:

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<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:

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<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 extension attributes, we need to use an after plugin on Product Repository. The plugin should be declared for the methods: save, get and getList.

We can add scalar and non-scalar extension attributes. Scalar is a simple attribute. Non-scalar attributes can be represented by Data Object.

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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;
}

This is the simplest way to add extension attributes without causing a conflict:

  • We get the entity’s extension attributes, if they are already set.
  • We add our extension attribute.
  • Finally set the extension attribute on the entity with ours included.

Function afterGetList is similar to afterGet:

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public function afterGetList(
    \Magento\Catalog\Api\ProductRepositoryInterface $subject,
    \Magento\Catalog\Api\Data\ProductSearchResultsInterface $searchCriteria
) : \Magento\Catalog\Api\Data\ProductSearchResultsInterface
{
    $products = [];
    foreach ($searchCriteria->getItems() as $entity) {
        $ourCustomData = $this->customDataRepository->get($entity->getId());

        $extensionAttributes = $entity->getExtensionAttributes();
        $extensionAttributes->setOurCustomData($ourCustomData);
        $entity->setExtensionAttributes($extensionAttributes);

        $products[] = $entity;
    }
    $searchCriteria->setItems($products);
    return $searchCriteria;
}

To add extension attributes to an entity without plugins, use the extensionActions argument of \Magento\Framework\EntityManager\Operation\ExtensionPool. See \Magento\Catalog\Model\ProductRepository::getList() as an example of an implementation.

Likewise, the afterSave plugin should manipulate the entity data before returning it:

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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 attributes we need to check if they are null. If so, then we need to create them. To avoid such code duplication, we need to create afterGetExtensionAttributes 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 look like this:

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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;
    }
}

Now we need to bind our plugin to ProductInterface:

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<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:

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<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="number" />
        <attribute code="second_custom_attribute" type="string" />
    </extension_attributes>
</config>

For non-scalar attributes:

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<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>

For array extension attributes:

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<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="some_custom_data" type="string[]" />
    </extension_attributes>
</config>

The array indicator [] can also be appended to non-scalar types.

In first - scalar - case we will get the next result:

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<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>foo</second_custom_attribute>
    </extension_attributes>
</product>

In second, non-scalar one:

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<product>
    <id>1</id>
    <sku>some-sku</sku>
    <custom_attributes><!-- Custom Attributes Data --></custom_attributes>
    <extension_attributes>
        <our_custom_data>
            <!-- fields defined in CustomDataInterface are here -->
        </our_custom_data>
    </extension_attributes>
</product>

In third, array one (in JSON for a change):

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{
  "id": 1,
  "sku": "some-sku",
  "custom_attributes": { /* ... custom attribute data ... */ },
  "extension_attributes": {
    "some_custom_data": ["value1", "value2", "value3"]
  }
}

Sample module on GitHub