Overlapping relationship represented by spring JPA - database

Question

I'm building a webpage backend from scratch as my first practice, using Spring boot, JPA and oracle database. Inside my database, there is a User table containing some information. And there are three other tables, Worker, Customer and Admin. A User can have several roles, for example, User can be both Worker and Admin. (I think it's a overlapping relationship as stated in EER diagram, correct me if I'm wrong)
Now I want to implement this relationship using JPA in Spring boot, but I don't know how exactly should I design the beans. Could someone give me a hint or similar example?
If spring JPA is not a good way to implement this kind of relationship, or if it's too complicate for me to understand. is there any better way to restructure my database table?
I've looked into JPA inheritance such as this post Spring Data Repository with Inheritance.JOINED but I didn't manage to make my code work, since I don't quite understand the mechanism behind
Here is a example of my database tables:
User(Id, username, password, ...)
Worker(Id, user_id, salary, ...)
Admin(Id, user_id, team_name, ...)
Customer(Id, user_id, account_balance, ...)
ps: As the homework requirement stated, I'm not suppose to use primary key or foreign key in the database since JPA can handle relationships.

Answer 1

user-> worker is one-one relationship as a user can be only one worker. the same applies to user-> admin and user-> customer. you can find mock-up code as below.
#Entity
#Table(name = "users")
public class User {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id")
private Long id;
//...
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "user_id")
private Worker worker;
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "user_id")
private Admin admin;
// ... getters and setters
}
#Entity
#Table(name = "worker")
public class Worker {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id")
private Long id;
//...
#OneToOne (mappedBy = "worker")
private User user;
}