WordPress REST API - Custom field not added to pages

Question

I have this code in my wordpress plugin. I'm working on an vue powered headless theme and I need to get all the informations about pages using the rest API.

I've registered with success a custom res field for a cpt, but now when I try to add a rest field for page object, it will be not added if I call the wp-json\wp\v2\pages I will not see the added field

function __construct()
{
  add_action('rest_api_init', [$this, 'setup_custom_routes']);
}

function setup_custom_routes(){

        register_rest_field( 
            'page', 
            'page_cover', 
            [
                'get_callback' => [$this, 'get_pages_cover']
            ] 
        );
}

function get_pages_cover( $post ){
    return get_the_post_thumbnail_url( $post['id'] );
}

Is there something wrong, or I need to do this in another way?

Answer 1

You may need to flush the REST API cache in order to see the added field. You can do this by adding the following code to your plugin:

This code will flush the REST API cache whenever a post (including a page) is saved or updated, so that the changes to the registered field will appear immediately.

If the field still does not appear after flushing the cache, you may want to check that the REST API request you're making is for a single page object and not a collection. The field will only be returned when you make a GET request for a single page, for example: wp-json/wp/v2/pages/123.

function flush_rest_api_cache() {
    wp_cache_flush();
}
add_action( 'save_post', 'flush_rest_api_cache' );