Magento 2 - extension attributes interface

Question

I'm trying to add an extension attribute to \Magento\Quote\Api\Data\TotalsInterface. My understanting is, that magento should generate getter/setter for the new attribute, but that is not happening. (i tried deleting var/generation var/cache multiple times)

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\Quote\Api\Data\TotalsInterface">        
        <attribute code="custom_attribute" type="string"/>
    </extension_attributes>
</config>

Is my understanding correct, or is this just not possible?

The interface is instantiated using factory in Magento\Quote\Model\Cart\CartTotalRepository. Could that have an effect?

Any help would be greatly appreciated.

Answer 1

The getters and setters are not added to the TotalsInterface itself.

Instead they are generated in Magento\Quote\Api\Data\TotalsExtensionInterface (which you should find in var/generation) and you use it like this (for custom_attribute):

$totals->getExtensionAttributes()->getCustomAttribute();