Entity relationships in JPA. Are two entities possible for one table?

Question

Java

I want such structure in java:
An abstract parent with a standard set of fields (id, name, etc). Entities are inherited from it and optionally add their fields.
In the database, it should look like this:
One common table for all entities inherited from Parent, and for those that have added their fields, separate tables with the InheritanceType.JOINED policy .

Those. for such a set of classes in the database there should be 2 tables:
parent and ch3 which has only id (link to the parent table) and extensionValue.
This is how an almost working scheme was added:
One abstract one with @MappedSuperclass, two abstract ones from it with different inheritance policies, and it is already final classes, but it doesn’t work exactly.
But it would be desirable without crutches.

Answer 1

Hello!
I recently started learning Spring Boot. And it's also interesting. And so I solved this issue as follows. In my case, these are 3 Entities - User, Customer, Author.

@Entity
@Data
@Table(name = "users")
@Inheritance(
        strategy = InheritanceType.JOINED
)
public class User {
  @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long userId;
    private String userEmail;
    private String userPassword;
    // getters setters etc.
}


@Entity
@Getter @Setter
@Table(name = "customers")
public class Customer extends User {
  private String customerData;
}


@Entity
@Getter @Setter
@Table(name = "authors")
public class Author extends User {
  private String authorData;
}

And in this case, you will get 3 tables. One common - User + 2 tables for Customer & Author, in which there will be an ID from the Entity User + additional. fields from child tables. Did you mean it?