Magento Shiksha

In Magento 2, Extension Attributes are a way to add custom fields or data to existing service contracts (like APIs, models, repositories) without directly modifying the core code.

They’re especially used when you want your custom data to be accessible through Magento’s Web APIs (REST/SOAP) or service contracts.

Key Points About Extension Attributes

• Introduced in Magento 2.1+.
• Added via extension_attributes.xml file.
• Works with service contracts (e.g., repositories like ProductRepository, OrderRepository).
• Data is stored in custom tables, not in the original entity table (like catalog_product_entity).
• Auto-generated getter and setter methods for your custom attribute.

When to Use

• When you want custom data available via API or in repository calls.
• When you want to separate custom data from the core Magento tables.
• Example: Adding a delivery_date attribute to an order.

Steps to Create an Extension Attribute

1. Create a Custom Table (optional)

If you need to store additional data:

CREATE TABLE custom_order_delivery_date (
entity_id INT AUTO_INCREMENT PRIMARY KEY,
order_id INT NOT NULL,
delivery_date DATETIME NULL,
FOREIGN KEY (order_id) REFERENCES sales_order(entity_id)
);

2. Define extension_attributes.xml

Create file:

app/code/Vendor/Module/etc/extension_attributes.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:framework:Api/etc/extension_attributes.xsd">
<extension_attributes for="Magento\Sales\Api\Data\OrderInterface">
<attribute code="delivery_date" type="string" />
</extension_attributes>
</config>

• for → Entity interface to extend (OrderInterface here).
• code → Your custom field name.
• type → Data type (string, int, bool, etc.).

3. Create Extension Attribute Getter/Setter

Magento automatically generates these methods:

$order->getExtensionAttributes()->getDeliveryDate();

$order->getExtensionAttributes()->setDeliveryDate('2025-09-01');

4. Load & Save Attribute Data

You need a plugin or observer to fetch/save the data from your custom table:

public function afterGet(\Magento\Sales\Api\OrderRepositoryInterface $subject, $order)
{
$extensionAttributes = $order->getExtensionAttributes();
if ($extensionAttributes === null) {
$extensionAttributes = $this->extensionAttributesFactory->create(\Magento\Sales\Api\Data\OrderInterface::class);
}
$deliveryDate = $this->customOrderRepository->getDeliveryDateByOrderId($order->getEntityId());
$extensionAttributes->setDeliveryDate($deliveryDate);
$order->setExtensionAttributes($extensionAttributes);
return $order;
}

This ensures the data shows up in APIs.

5. Check in API Response

After clearing cache and running bin/magento setup:upgrade,

GET /V1/orders/:id will now return:

{
"entity_id": 1,
"increment_id": "000000001",
"extension_attributes": {
"delivery_date": "2025-09-01"
}
}