Add Custom Data to Rest Api response

Question

I tried to add custom data to the endpoint V1/categories but ended up with getting error

My code is below

1. etc/extension_attributes.xml

<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\CategoryRepositoryInterface">
        <attribute code="banner_slider" type="string" />
    </extension_attributes>
</config>

2.di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Catalog\Api\CategoryRepositoryInterface">
        <plugin name="banner_image_data" type="Vendor\ModuleName\Plugin\Model\CategoryRepository"/>
    </type>
</config>

3.Plugin

use Magento\Catalog\Model\CategoryRepository as Subject;

class CategoryRepository
{

    /**
     * @param Subject $subject
     * @param CategoryInterface $data
     * @return CategoryInterface
     */
    public function afterGet(
        Subject $subject,
        CategoryInterface $data
    )
    {
        $extensionAttributes = $data->getExtensionAttributes();
        $extensionAttributes->setBannerSlider('sandesh');
        $data->setExtensionAttributes($extensionAttributes);
        return $data;
    }
}

My error

 Call to undefined method Magento\Catalog\Api\Data\CategoryExtension::setBannerSlider()

Answer 1

Please replace your files with the following code:

1.etc/extension_attributes.xml

<extension_attributes for="Magento\Catalog\Api\Data\CategoryInterface">
        <attribute code="banner_slider" type="string" />
    </extension_attributes>

2.di.xml

<type name="Magento\Catalog\Api\CategoryRepositoryInterface">
        <plugin name="banner_image_data" type="Vendor\ModuleName\Plugin\Model\CategoryRepository"/>
    </type>

3.Plugin

<?php
namespace Vendor\ModuleName\Plugin\Model;
use Magento\Catalog\Api\CategoryRepositoryInterface as Subject;

class CategoryRepository
{

    /**
     * @param Subject $subject
     * @param CategoryInterface $data
     * @return CategoryInterface
     */
    public function afterGet(
        Subject $subject,
        \Magento\Catalog\Api\Data\CategoryInterface $data
    )
    {
        $extensionAttributes = $data->getExtensionAttributes();
        $extensionAttributes->setBannerSlider('sandesh');
        $data->setExtensionAttributes($extensionAttributes);
        return $data;
    }
}
?>

let me know if you need any further assistanse. don't forget to upvote and mark as answer :)