public function add( $args, $assoc_args ) {
		list( $object_id, $meta_key ) = $args;

		$meta_value = WP_CLI::get_value_from_arg_or_stdin( $args, 2 );
		$meta_value = WP_CLI::read_value( $meta_value, $assoc_args );

		$object_id = $this->check_object_id( $object_id );

		$meta_value = wp_slash( $meta_value );
		$success    = $this->add_metadata( $object_id, $meta_key, $meta_value );

		if ( $success ) {
			WP_CLI::success( 'Added custom field.' );
		} else {
			WP_CLI::error( 'Failed to add custom field.' );
		}
	}