CREATE TABLE `Notification` (
	`id` int,
	`sender_id` int,
	`recipient_id` int,
	`object_id` int,
	`object_type` varchar(255),
	`is_read` bool,
	`date_created` datetime,
	FOREIGN KEY(`sender_id`) REFERENCES `User` (`id`)
);
CREATE TABLE `User` (
	`id` int,
	`username` varchar(255)
);