Filter results to children post items (Types plugin)

gistfile1.php

<?php
/**
 * Context:
 * Using the Types plugin, the "Resources" post type is a child of the "Courses" post type.
 * On a Course page, show only Resources belonging to the current Course
 * 
 * _wpcf_belongs_courses_id
 * This custom field stores the ID of a Resource's parent Course
 */

// Get the Course slug from the URL
$uri = explode('/', $this->http_params['uri'] );
$slug = array_pop( $uri );

// Get the Course ID from the slug
$result = get_posts( array( 'post_type' => 'courses', 'name' => $slug, 'posts_per_page' => 1 ) );
$course_id = empty( $result ) ? array() : $result[0]->ID;

return array(
  'post_type' => 'resource',
  'posts_per_page' => 100,
  'meta_query' => array(
    array(
      'key' => '_wpcf_belongs_courses_id', // Show Resources belonging to the the current Course
      'value' => $course_id,
    )
  )
);