*
	 * @param WP_REST_Request $request Full details about the request.
	 * @return array|WP_Error
	 */
	protected function prepare_collection_query_args( $request ) {

		$query_args = parent::prepare_collection_query_args( $request );
		if ( is_wp_error( $query_args ) ) {
			return $query_args;
		}

		// Orderby 'order' requires a meta query.
		if ( isset( $query_args['orderby'] ) && 'order' === $query_args['orderby'] ) {
			$query_args = array_merge(
				$query_args,
				array(
					'meta_key' => '_llms_order',
					'orderby'  => 'meta_value_num',
				)
			);
		}

		if ( isset( $this->parent_id ) ) {
			$parent_id = $this->parent_id;
		} elseif ( ! empty( $request['parent'] ) && $request['parent'] > 1 ) {
			$parent_id = $request['parent'];
		}

		// Filter by parent.
		if ( ! empty( $parent_id ) ) {
			$query_args = array_merge(
				$query_args,
				array(
					'meta_query' => array(
						array(
							'key'     => '_llms_parent_course',
							'value'   => $parent_id,
							'compare' => '=',
						),
					),
				)
			);