Adding meta fields with orderby endpoint to WordPress rest API

Adding-meta-fields-with-orderby-endpoint-to-WordPress-rest_API.php

<?php
// Register the meta field for the rest api
// https://stackoverflow.com/questions/56460557/how-to-include-meta-fields-in-wordpress-api-post#answer-56508996
add_action( 'rest_api_init', 'register_postviews_meta_fields');
function register_postviews_meta_fields(){

    register_meta( 'post', 'wpb_post_views_count', array(
        'type' => 'integer',
        'description' => 'Post views',
        'single' => true,
        'show_in_rest' => true
	));
}

//https://github.com/WP-API/WP-API/issues/2308#issuecomment-262886432
add_filter('rest_endpoints', function ($routes) {
	// I'm modifying multiple types here, you won't need the loop if you're just doing posts
	foreach (['post'] as $type) {
		if (!($route =& $routes['/wp/v2/' . $type])) {
			continue;
		}

		// Allow ordering by my meta value
		$route[0]['args']['orderby']['enum'][] = 'meta_value_num';

		// Allow only the meta keys that I want
		$route[0]['args']['meta_key'] = array(
			'description'       => 'The meta key to query.',
			'type'              => 'string',
			'enum'              => ['wpb_post_views_count'],
			'validate_callback' => 'rest_validate_request_arg',
		);
	}

	return $routes;
});

//https://github.com/WP-API/WP-API/issues/2308#issuecomment-265875108
add_filter('rest_post_query', function ($args, $request) {
	if ($key = $request->get_param('meta_key')) {
		$args['meta_key'] = $key;
	}
	return $args;
}, 10, 2);


// This enables the orderby=menu_order for Posts
// https://www.timrosswebdevelopment.com/wordpress-rest-api-post-order/
add_filter( 'rest_post_collection_params', 'filter_add_rest_orderby_params', 10, 1 );
// And this for a custom post type called 'portfolio'
// add_filter( 'rest_portfolio_collection_params', 'filter_add_rest_orderby_params', 10, 1 );
/**
 * Add menu_order to the list of permitted orderby values
 */
function filter_add_rest_orderby_params( $params ) {
	$params['orderby']['enum'][] = 'meta_value_num';
	return $params;
}