public function register_meta() {

		foreach ( $this->post_types as $post_type ) {

			register_rest_field(
				$post_type,
				'instructors',
				array(
					'get_callback'    => array( $this, 'get_callback' ),
					'update_callback' => array( $this, 'update_callback' ),
					'schema'          => null,
				)
			);

		}

	}