To design a comprehensive database for the notifications of a social media app, we'll need to create several tables to capture the various aspects of the notification system. Here's a suggested database design:

1. Table: Users

• user_id (Primary Key, Auto Increment)
• username
• email
• password
• created_at

1. Table: Posts

• post_id (Primary Key, Auto Increment)
• user_id (Foreign Key referencing Users)
• content
• image_url (optional)
• created_at

1. Table: Comments

• comment_id (Primary Key, Auto Increment)
• post_id (Foreign Key referencing Posts)
• user_id (Foreign Key referencing Users)
• content
• created_at

1. Table: Follows

• follow_id (Primary Key, Auto Increment)
• follower_id (Foreign Key referencing Users)
• following_id (Foreign Key referencing Users)
• created_at

1. Table: Notification_Types

• type_id (Primary Key, Auto Increment)
• name (e.g., 'comment', 'like', 'follow')
• description
• redirect_url (url template for redirecting the user when clicked, e.g., '/posts/{post_id}' or '/profile/{user_id}')

1. Table: Notifications

• notification_id (Primary Key, Auto Increment)
• user_id (Foreign Key referencing Users)
• type_id (Foreign Key referencing Notification_Types)
• source_user_id (Foreign Key referencing Users, the user who initiated the action)
• post_id (Foreign Key referencing Posts, NULL if not applicable)
• comment_id (Foreign Key referencing Comments, NULL if not applicable)
• follow_id (Foreign Key referencing Follows, NULL if not applicable)
• received_at
• read_at (NULL if unread)

With this design, you can create notifications for various scenarios like a user commenting on a post, someone liking a post, or someone starting to follow another user. The Notification_Types table can be extended to include more notification types as needed.

The Notifications table captures whether the notification has been read or not, using the read_at column. If the read_at value is NULL, the notification is considered unread.

To redirect users to specific pages when they click on a notification, you can use the redirect_url from the Notification_Types table, replacing placeholders (e.g., '{post_id}', '{user_id}') with actual values from the relevant record.

As you mentioned, social media notification functionality can have many more features. Depending on the specific features, additional tables or columns may be needed. However, this design provides a good foundation to build upon.

Here's the PostgreSQL script for creating the tables based on the above database design:

sqlCopy code
-- Create Users table
CREATE TABLE users (
    user_id SERIAL PRIMARY KEY,
    username VARCHAR(255) NOT NULL,
    email VARCHAR(255) NOT NULL UNIQUE,
    password VARCHAR(255) NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
);

-- Create Posts table
CREATE TABLE posts (
    post_id SERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL,
    content TEXT NOT NULL,
    image_url VARCHAR(255),
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES users (user_id)
);

-- Create Comments table
CREATE TABLE comments (
    comment_id SERIAL PRIMARY KEY,
    post_id INTEGER NOT NULL,
    user_id INTEGER NOT NULL,
    content TEXT NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (post_id) REFERENCES posts (post_id),
    FOREIGN KEY (user_id) REFERENCES users (user_id)
);

-- Create Follows table
CREATE TABLE follows (
    follow_id SERIAL PRIMARY KEY,
    follower_id INTEGER NOT NULL,
    following_id INTEGER NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (follower_id) REFERENCES users (user_id),
    FOREIGN KEY (following_id) REFERENCES users (user_id)
);

-- Create Notification_Types table
CREATE TABLE notification_types (
    type_id SERIAL PRIMARY KEY,
    name VARCHAR(255) NOT NULL UNIQUE,
    description TEXT,
    redirect_url VARCHAR(255) NOT NULL
);

-- Create Notifications table
CREATE TABLE notifications (
    notification_id SERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL,
    type_id INTEGER NOT NULL,
    source_user_id INTEGER NOT NULL,
    post_id INTEGER,
    comment_id INTEGER,
    follow_id INTEGER,
    received_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    read_at TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES users (user_id),
    FOREIGN KEY (type_id) REFERENCES notification_types (type_id),
    FOREIGN KEY (source_user_id) REFERENCES users (user_id),
    FOREIGN KEY (post_id) REFERENCES posts (post_id),
    FOREIGN KEY (comment_id) REFERENCES comments (comment_id),
    FOREIGN KEY (follow_id) REFERENCES follows (follow_id)
);

This script creates the tables according to the database design provided. You can run the script in a PostgreSQL client or pgAdmin to create the tables in your database.

Apologies for the confusion. You are correct that the follow_id column in the notifications table may not be necessary in this particular design.

The follow_id column was included to capture the specific follow relationship that triggered the notification, but since the source_user_id already captures the user who initiated the action (i.e., started following another user), the follow_id is redundant.

You can remove the follow_id column from the notifications table, and the modified Notifications table schema would look like this:

sqlCopy code
-- Create Notifications table (updated)
CREATE TABLE notifications (
    notification_id SERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL,
    type_id INTEGER NOT NULL,
    source_user_id INTEGER NOT NULL,
    post_id INTEGER,
    comment_id INTEGER,
    received_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    read_at TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES users (user_id),
    FOREIGN KEY (type_id) REFERENCES notification_types (type_id),
    FOREIGN KEY (source_user_id) REFERENCES users (user_id),
    FOREIGN KEY (post_id) REFERENCES posts (post_id),
    FOREIGN KEY (comment_id) REFERENCES comments (comment_id)
);

This updated design should still capture all the necessary information to create notifications for various scenarios without redundancy.

After reviewing the database design, I believe the current design is now appropriate without any unnecessary columns. Each column serves a purpose in capturing the required information for different scenarios of notifications and other aspects of a social media app.

However, it's important to note that the specific requirements of your application might affect which columns are necessary or not. It's always a good idea to analyze your requirements thoroughly and adapt the design accordingly. If you identify any changes in your application's needs or features, you may need to update the database design to better suit those requirements.

I'm unable to directly interact with a PostgreSQL database or simulate data flow in real-time. However, I can provide you with example SQL scripts to illustrate how the data could be inserted into the tables for various notification scenarios.

Let's assume we have the following data:

1. Two users (User A and User B)
2. One post created by User A
3. User B follows User A
4. User B likes User A's post
5. User B comments on User A's post

First, we'll insert the data into the respective tables:

sqlCopy code
-- Insert users
INSERT INTO users (username, email, password) VALUES
('User A', 'user_a@example.com', 'passwordA'),
('User B', 'user_b@example.com', 'passwordB');

-- Insert a post by User A
INSERT INTO posts (user_id, content) VALUES
(1, 'This is a post by User A.');

-- User B follows User A
INSERT INTO follows (follower_id, following_id) VALUES
(2, 1);

-- Insert notification_types
INSERT INTO notification_types (name, description, redirect_url) VALUES
('follow', 'A user started following you', '/profile/{user_id}'),
('like', 'A user liked your post', '/posts/{post_id}'),
('comment', 'A user commented on your post', '/posts/{post_id}');

-- Assuming we have a separate table for post_likes (as it's not in the original design)
-- Insert a like by User B on User A's post
INSERT INTO post_likes (post_id, user_id) VALUES
(1, 2);

-- Insert a comment by User B on User A's post
INSERT INTO comments (post_id, user_id, content) VALUES
(1, 2, 'This is a comment by User B.');

Now, we'll insert notifications for each action:

sqlCopy code
-- Notification for User B following User A
INSERT INTO notifications (user_id, type_id, source_user_id) VALUES
(1, 1, 2);

-- Notification for User B liking User A's post
INSERT INTO notifications (user_id, type_id, source_user_id, post_id) VALUES
(1, 2, 2, 1);

-- Notification for User B commenting on User A's post
INSERT INTO notifications (user_id, type_id, source_user_id, post_id, comment_id) VALUES
(1, 3, 2, 1, 1);

Now you should have three notifications for User A, one for each scenario (follow, like, and comment). When implementing this in an actual application, you would write backend code (e.g., in Python, Node.js, or another language) to handle the process of inserting data and creating notifications when users perform these actions.

To avoid hardcoding IDs in the insert statements for notifications, you can use subqueries to fetch the relevant IDs from the other tables. Here's the updated script for inserting notifications based on actions without hardcoding IDs:

sqlCopy code
-- Notification for User B following User A
INSERT INTO notifications (user_id, type_id, source_user_id)
VALUES (
  (SELECT user_id FROM users WHERE username = 'User A'),
  (SELECT type_id FROM notification_types WHERE name = 'follow'),
  (SELECT user_id FROM users WHERE username = 'User B')
);

-- Notification for User B liking User A's post
INSERT INTO notifications (user_id, type_id, source_user_id, post_id)
VALUES (
  (SELECT user_id FROM users WHERE username = 'User A'),
  (SELECT type_id FROM notification_types WHERE name = 'like'),
  (SELECT user_id FROM users WHERE username = 'User B'),
  (SELECT post_id FROM posts WHERE user_id = (SELECT user_id FROM users WHERE username = 'User A') LIMIT 1)
);

-- Notification for User B commenting on User A's post
INSERT INTO notifications (user_id, type_id, source_user_id, post_id, comment_id)
VALUES (
  (SELECT user_id FROM users WHERE username = 'User A'),
  (SELECT type_id FROM notification_types WHERE name = 'comment'),
  (SELECT user_id FROM users WHERE username = 'User B'),
  (SELECT post_id FROM posts WHERE user_id = (SELECT user_id FROM users WHERE username = 'User A') LIMIT 1),
  (SELECT comment_id FROM comments WHERE user_id = (SELECT user_id FROM users WHERE username = 'User B') AND post_id = (SELECT post_id FROM posts WHERE user_id = (SELECT user_id FROM users WHERE username = 'User A') LIMIT 1) LIMIT 1)
);

This script fetches the required IDs from the tables using subqueries based on the usernames, post and comment content, and notification type names. Note that this is just an example, and in a real application, you should ideally handle this process through backend code instead of relying on content matching.

Sure, I can update the complete database design to include the notification_types table. Here's the updated database design:

1. Table: Users

• user_id (Primary Key, Auto Increment)
• username
• email
• password
• created_at

1. Table: Posts

• post_id (Primary Key, Auto Increment)
• user_id (Foreign Key referencing Users)
• content
• image_url (optional)
• created_at

1. Table: Comments

• comment_id (Primary Key, Auto Increment)
• post_id (Foreign Key referencing Posts)
• user_id (Foreign Key referencing Users)
• content
• created_at

1. Table: Follows

• follow_id (Primary Key, Auto Increment)
• follower_id (Foreign Key referencing Users)
• following_id (Foreign Key referencing Users)
• created_at

1. Table: Notifications

• notification_id (Primary Key, Auto Increment)
• user_id (Foreign Key referencing Users)
• type_id (Foreign Key referencing Notification_Types)
• source_user_id (Foreign Key referencing Users, the user who initiated the action)
• post_id (Foreign Key referencing Posts, NULL if not applicable)
• comment_id (Foreign Key referencing Comments, NULL if not applicable)
• follow_id (Foreign Key referencing Follows, NULL if not applicable)
• received_at
• read_at (NULL if unread)

1. Table: Notification_Types

• type_id (Primary Key, Auto Increment)
• name (e.g., 'comment', 'like', 'follow')
• description
• redirect_url (url template for redirecting the user when clicked, e.g., '/posts/{post_id}' or '/profile/{user_id}')

With this updated design, the notification types are stored in the Notification_Types table. Each notification in the Notifications table references a notification type by its type_id. The Notification_Types table includes a description of each notification type and a redirect URL that can be used to redirect the user to the relevant page when they click on a notification.

You can use this design to create notifications for various scenarios, and add or modify notification types as needed in the Notification_Types table.

I apologize for the confusion. The follow_id column in the Notifications table is not needed in this updated database design, as it can be derived from the source_user_id and the user_id columns.

The source_user_id column captures the user who initiated the action (i.e., started following another user), and the user_id column captures the user who receives the notification. Therefore, when a user receives a follow notification, the follow relationship can be derived from the source_user_id and user_id columns.

As such, the Notifications table can be updated to remove the follow_id column. Here's the updated Notifications table schema:

sqlCopy code
-- Create Notifications table (updated)
CREATE TABLE notifications (
    notification_id SERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL,
    type_id INTEGER NOT NULL,
    source_user_id INTEGER NOT NULL,
    post_id INTEGER,
    comment_id INTEGER,
    received_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    read_at TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES users (user_id),
    FOREIGN KEY (type_id) REFERENCES notification_types (type_id),
    FOREIGN KEY (source_user_id) REFERENCES users (user_id),
    FOREIGN KEY (post_id) REFERENCES posts (post_id),
    FOREIGN KEY (comment_id) REFERENCES comments (comment_id)
);

I hope this clears up any confusion. Thank you for bringing this to my attention.

Sure! Here's the complete PostgreSQL script for the finalized database design:

sqlCopy code
-- Create Users table
CREATE TABLE Users (
    user_id SERIAL PRIMARY KEY,
    username VARCHAR(255) NOT NULL,
    email VARCHAR(255) NOT NULL UNIQUE,
    password VARCHAR(255) NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
);

-- Create Posts table
CREATE TABLE Posts (
    post_id SERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL,
    content TEXT NOT NULL,
    image_url VARCHAR(255),
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES Users (user_id)
);

-- Create Comments table
CREATE TABLE Comments (
    comment_id SERIAL PRIMARY KEY,
    post_id INTEGER NOT NULL,
    user_id INTEGER NOT NULL,
    content TEXT NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (post_id) REFERENCES Posts (post_id),
    FOREIGN KEY (user_id) REFERENCES Users (user_id)
);

-- Create Follows table
CREATE TABLE Follows (
    follow_id SERIAL PRIMARY KEY,
    follower_id INTEGER NOT NULL,
    following_id INTEGER NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (follower_id) REFERENCES Users (user_id),
    FOREIGN KEY (following_id) REFERENCES Users (user_id)
);

-- Create Notification_Types table
CREATE TABLE Notification_Types (
    type_id SERIAL PRIMARY KEY,
    name VARCHAR(255) NOT NULL UNIQUE,
    description TEXT,
    redirect_url VARCHAR(255) NOT NULL
);

-- Create Notifications table
CREATE TABLE Notifications (
    notification_id SERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL,
    type_id INTEGER NOT NULL,
    source_user_id INTEGER NOT NULL,
    post_id INTEGER,
    comment_id INTEGER,
    received_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    read_at TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES Users (user_id),
    FOREIGN KEY (type_id) REFERENCES Notification_Types (type_id),
    FOREIGN KEY (source_user_id) REFERENCES Users (user_id),
    FOREIGN KEY (post_id) REFERENCES Posts (post_id),
    FOREIGN KEY (comment_id) REFERENCES Comments (comment_id)
);

This script creates all the tables and their relationships based on the finalized database design. You can run this script in a PostgreSQL client or pgAdmin to create the tables in your database.

Sure! Here's an example script to insert data into the tables based on the notification flow you provided. This script uses subqueries to fetch the relevant IDs from the other tables instead of hardcoding them:

sqlCopy code
-- Insert users
INSERT INTO Users (username, email, password) VALUES
('User A', 'user_a@example.com', 'passwordA'),
('User B', 'user_b@example.com', 'passwordB');

-- Insert a post by User A
INSERT INTO Posts (user_id, content) VALUES
((SELECT user_id FROM Users WHERE username = 'User A'), 'This is a post by User A.');

-- User B follows User A
INSERT INTO Follows (follower_id, following_id) VALUES
((SELECT user_id FROM Users WHERE username = 'User B'), (SELECT user_id FROM Users WHERE username = 'User A'));

-- Insert notification_types
INSERT INTO Notification_Types (name, description, redirect_url) VALUES
('follow', 'A user started following you', '/profile/{user_id}'),
('like', 'A user liked your post', '/posts/{post_id}'),
('comment', 'A user commented on your post', '/posts/{post_id}');

-- Assuming we have a separate table for post_likes (as it's not in the original design)
-- Insert a like by User B on User A's post
INSERT INTO post_likes (post_id, user_id) VALUES
((SELECT post_id FROM Posts WHERE user_id = (SELECT user_id FROM Users WHERE username = 'User A') LIMIT 1), (SELECT user_id FROM Users WHERE username = 'User B'));

-- Insert a comment by User B on User A's post
INSERT INTO Comments (post_id, user_id, content) VALUES
((SELECT post_id FROM Posts WHERE user_id = (SELECT user_id FROM Users WHERE username = 'User A') LIMIT 1), (SELECT user_id FROM Users WHERE username = 'User B'), 'This is a comment by User B.');

-- Insert notifications
INSERT INTO Notifications (user_id, type_id, source_user_id, post_id, comment_id) VALUES
(
    (SELECT user_id FROM Users WHERE username = 'User A'), 
    (SELECT type_id FROM Notification_Types WHERE name = 'follow'), 
    (SELECT user_id FROM Users WHERE username = 'User B'), 
    NULL, 
    NULL
);

INSERT INTO Notifications (user_id, type_id, source_user_id, post_id, comment_id) VALUES
(
    (SELECT user_id FROM Users WHERE username = 'User A'), 
    (SELECT type_id FROM Notification_Types WHERE name = 'like'), 
    (SELECT user_id FROM Users WHERE username = 'User B'), 
    (SELECT post_id FROM Posts WHERE user_id = (SELECT user_id FROM Users WHERE username = 'User A') LIMIT 1), 
    NULL
);

INSERT INTO Notifications (user_id, type_id, source_user_id, post_id, comment_id) VALUES
(
    (SELECT user_id FROM Users WHERE username = 'User A'), 
    (SELECT type_id FROM Notification_Types WHERE name = 'comment'), 
    (SELECT user_id FROM Users WHERE username = 'User B'), 
    (SELECT post_id FROM Posts WHERE user_id = (SELECT user_id FROM Users WHERE username = 'User A') LIMIT 1), 
    (SELECT comment_id FROM Comments WHERE user_id = (SELECT user_id FROM Users WHERE username = 'User B') AND post_id = (SELECT post_id FROM Posts WHERE user_id = (SELECT user_id FROM Users WHERE username = 'User A') LIMIT 1) LIMIT 1)
);

This script inserts data into the tables using subqueries to fetch the relevant IDs

Sure, I can update the database design to include the post_likes table. Here's the updated design and the PostgreSQL script to create the tables:

1. Table: Users

• user_id (Primary Key, Auto Increment)
• username
• email
• password
• created_at

1. Table: Posts

• post_id (Primary Key, Auto Increment)
• user_id (Foreign Key referencing Users)
• content
• image_url (optional)
• created_at

1. Table: Comments

• comment_id (Primary Key, Auto Increment)
• post_id (Foreign Key referencing Posts)
• user_id (Foreign Key referencing Users)
• content
• created_at

1. Table: Follows

• follow_id (Primary Key, Auto Increment)
• follower_id (Foreign Key referencing Users)
• following_id (Foreign Key referencing Users)
• created_at

1. Table: Notifications

• notification_id (Primary Key, Auto Increment)
• user_id (Foreign Key referencing Users)
• type_id (Foreign Key referencing Notification_Types)
• source_user_id (Foreign Key referencing Users, the user who initiated the action)
• post_id (Foreign Key referencing Posts, NULL if not applicable)
• comment_id (Foreign Key referencing Comments, NULL if not applicable)
• received_at
• read_at (NULL if unread)

1. Table: Notification_Types

• type_id (Primary Key, Auto Increment)
• name (e.g., 'comment', 'like', 'follow')
• description
• redirect_url (url template for redirecting the user when clicked, e.g., '/posts/{post_id}' or '/profile/{user_id}')

1. Table: Post_Likes

• post_id (Primary Key, Foreign Key referencing Posts)
• user_id (Primary Key, Foreign Key referencing Users)
• created_at

And here's the updated PostgreSQL script to create the tables:

sqlCopy code
-- Create Users table
CREATE TABLE Users (
    user_id SERIAL PRIMARY KEY,
    username VARCHAR(255) NOT NULL,
    email VARCHAR(255) NOT NULL UNIQUE,
    password VARCHAR(255) NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
);

-- Create Posts table
CREATE TABLE Posts (
    post_id SERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL,
    content TEXT NOT NULL,
    image_url VARCHAR(255),
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES Users (user_id)
);

-- Create Comments table
CREATE TABLE Comments (
    comment_id SERIAL PRIMARY KEY,
    post_id INTEGER NOT NULL,
    user_id INTEGER NOT NULL,
    content TEXT NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (post_id) REFERENCES Posts (post_id),
    FOREIGN KEY (user_id) REFERENCES Users (user_id)
);

-- Create Follows table
CREATE TABLE Follows (
    follow_id SERIAL PRIMARY KEY,
    follower_id INTEGER NOT NULL,
    following_id INTEGER NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (follower_id) REFERENCES Users (user_id),
    FOREIGN KEY (following_id) REFERENCES Users (user_id)
);

-- Create Notifications table
CREATE TABLE Notifications (
    notification_id SERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL,
    type_id INTEGER NOT NULL,
    source_user_id INTEGER NOT NULL,
    post_id INTEGER,
    comment_id INTEGER,
    received_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    read_at TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES Users (user_id),
    FOREIGN KEY (type_id) REFERENCES Notification_Types (type_id),
    FOREIGN KEY (source_user_id) REFERENCES Users (user_id),
    FOREIGN KEY (post_id) REFERENCES Posts (post_id),
    FOREIGN KEY (comment_id

Sure, here's the PostgreSQL script to create the Post_Likes table:

sqlCopy code
-- Create Post_Likes table
CREATE TABLE Post_Likes (
    post_id INTEGER NOT NULL,
    user_id INTEGER NOT NULL,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY (post_id, user_id),
    FOREIGN KEY (post_id) REFERENCES Posts (post_id),
    FOREIGN KEY (user_id) REFERENCES Users (user_id)
);

This script creates the Post_Likes table with a composite primary key made up of the post_id and user_id columns. It also adds foreign key constraints to reference the Posts and Users tables.

Sure, here's an example implementation of the Spring Boot JPA entities for the finalized database design:

1. User entity:

javaCopy code
@Entity
@Table(name = "Users")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "user_id")
    private Long userId;

    @Column(name = "username")
    private String username;

    @Column(name = "email")
    private String email;

    @Column(name = "password")
    private String password;

    @Column(name = "created_at")
    private LocalDateTime createdAt;

    // getters and setters
}

1. Post entity:

javaCopy code
@Entity
@Table(name = "Posts")
public class Post {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "post_id")
    private Long postId;

    @ManyToOne
    @JoinColumn(name = "user_id", referencedColumnName = "user_id")
    private User user;

    @Column(name = "content")
    private String content;

    @Column(name = "image_url")
    private String imageUrl;

    @Column(name = "created_at")
    private LocalDateTime createdAt;

    // getters and setters
}

1. Comment entity:

javaCopy code
@Entity
@Table(name = "Comments")
public class Comment {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "comment_id")
    private Long commentId;

    @ManyToOne
    @JoinColumn(name = "post_id", referencedColumnName = "post_id")
    private Post post;

    @ManyToOne
    @JoinColumn(name = "user_id", referencedColumnName = "user_id")
    private User user;

    @Column(name = "content")
    private String content;

    @Column(name = "created_at")
    private LocalDateTime createdAt;

    // getters and setters
}

1. Follow entity:

javaCopy code
@Entity
@Table(name = "Follows")
public class Follow {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "follow_id")
    private Long followId;

    @ManyToOne
    @JoinColumn(name = "follower_id", referencedColumnName = "user_id")
    private User follower;

    @ManyToOne
    @JoinColumn(name = "following_id", referencedColumnName = "user_id")
    private User following;

    @Column(name = "created_at")
    private LocalDateTime createdAt;

    // getters and setters
}

1. Notification entity:

javaCopy code
@Entity
@Table(name = "Notifications")
public class Notification {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "notification_id")
    private Long notificationId;

    @ManyToOne
    @JoinColumn(name = "user_id", referencedColumnName = "user_id")
    private User user;

    @ManyToOne
    @JoinColumn(name = "type_id", referencedColumnName = "type_id")
    private NotificationType type;

    @ManyToOne
    @JoinColumn(name = "source_user_id", referencedColumnName = "user_id")
    private User sourceUser;

    @ManyToOne
    @JoinColumn(name = "post_id", referencedColumnName = "post_id")
    private Post post;

    @ManyToOne
    @JoinColumn(name = "comment_id", referencedColumnName = "comment_id")
    private Comment comment;

    @Column(name = "received_at")
    private LocalDateTime receivedAt;

    @Column(name = "read_at")
    private LocalDateTime readAt;

    // getters and setters
}

1. NotificationType entity:

javaCopy code
@Entity
@Table(name = "Notification_Types")
public class NotificationType {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "type_id")
    private Long typeId;

    @Column(name = "name")
    private

No, that's not all. There's one more entity that we need to add for the Post_Likes table.

1. PostLike entity:

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@Entity
@Table(name = "Post_Likes")
public class PostLike {

    @EmbeddedId
    private PostLikeId id;

    @ManyToOne
    @MapsId("postId")
    @JoinColumn(name = "post_id")
    private Post post;

    @ManyToOne
    @MapsId("userId")
    @JoinColumn(name = "user_id")
    private User user;

    @Column(name = "created_at")
    private LocalDateTime createdAt;

    // getters and setters
}

This entity is used to represent the composite primary key for the Post_Likes table. The @EmbeddedId annotation is used to specify that this entity has a composite primary key made up of the postId and userId columns. The @MapsId annotation is used to map the postId and userId fields to the corresponding fields in the PostLikeId class.

Here's the PostLikeId class:

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@Embeddable
public class PostLikeId implements Serializable {

    private static final long serialVersionUID = 1L;

    @Column(name = "post_id")
    private Long postId;

    @Column(name = "user_id")
    private Long userId;

    // getters and setters
}

This class is used as the composite primary key for the Post_Likes table. It has two fields (postId and userId) that correspond to the two columns in the composite primary key. The @Embeddable annotation is used to specify that this class can be embedded in other entities.

I apologize for the mistake. Here's the complete NotificationType entity:

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@Entity
@Table(name = "Notification_Types")
public class NotificationType {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "type_id")
    private Long typeId;

    @Column(name = "name")
    private String name;

    @Column(name = "description")
    private String description;

    @Column(name = "redirect_url")
    private String redirectUrl;

    // getters and setters
}

This entity represents the Notification_Types table in the database. It has four fields (typeId, name, description, and redirectUrl) that correspond to the columns in the Notification_Types table. The typeId field is annotated with @Id and @GeneratedValue to specify that it is the primary key for the entity and that its value is generated automatically by the database. The other fields are annotated with @Column to specify their corresponding column names in the database.

Sure! Here's an example of an application.properties file for configuring a PostgreSQL server in a Spring Boot application:

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# Database configuration
spring.datasource.url=jdbc:postgresql://localhost:5432/dbname
spring.datasource.username=postgres
spring.datasource.password=password

# Hibernate configuration
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.format_sql=true

In this example, we're using the spring.datasource prefix to configure the connection to the PostgreSQL database. We're specifying the URL of the database, the username and password for the database user, and the dialect for Hibernate to use.

We're also setting some properties for Hibernate to use, such as spring.jpa.hibernate.ddl-auto, which specifies the DDL mode, spring.jpa.show-sql, which determines whether SQL statements should be logged, and spring.jpa.properties.hibernate.format_sql, which formats the SQL statements for better readability.

You'll need to replace dbname, postgres, and password with the actual name of your database, the username and password for your PostgreSQL user, respectively.