Change a REST API field value - Change the value of a field in a REST API endpoint. https://www.damiencarbery.com/2026/05/change-a-rest-api-field-value/

rest-api-change-field-value.php

<?php
/*
Plugin Name: REST API - change field value
Plugin URI: https://www.damiencarbery.com
Description: Change the value of a field in a REST API endpoint.
Author: Damien Carbery
Version: 0.1.20260522
*/


class RestApiAddField {
	private $post_type;
	private $field_to_change;


	// Returns an instance of this class. 
	public static function get_instance() {
		if ( null == self::$instance ) {
			self::$instance = new self;
		} 
		return self::$instance;
	}


	// Initialize the plugin variables.
	public function __construct() {
		// Set the post type that we will access.
		$this->post_type = 'post';
		// And the REST API field we are changing.
		$this->field_to_change = 'link';

		$this->init();
	}


	// Set up WordPress specfic actions.
	public function init() {
		add_action( 'rest_api_init', array( $this, 'change_rest_api_link_field' ) );
	}


	public function change_rest_api_link_field() {
		register_rest_field( $this->post_type, $this->field_to_change, array(
			'get_callback' => array( $this, 'get_link_for_rest_api' ),
			)
		);
	}


	public function get_link_for_rest_api( $object, $request ) {
		//error_log( '$request: ' . var_export( $request, true ) );
		//error_log( '$object: ' . var_export( $object, true ) );

		// Get the id of the post from the object array if needed.
		//$post_id = $object['id'];

		if ( $this->field_to_change == $request ) {
			return str_replace( home_url(), 'https://example.com', $object['link'] );
		}

		// If you use the same callback to process another field then check $request.
		/*if ( 'guid' == $request ) {
			return $object[ $request ] . '&extra=more_data';
		}*/

		return $object[ $request ];
	}
}
$RestApiAddField = new RestApiAddField();