JPA Inheritance demands ID in subclass

Question

I have a problem with my jpa domain model. I am just trying to play around with simple inheritance for which I use a simple Person base-class and and a Customer subclass. According to the official documentation (both, JPA and EclipseLink) I only need the ID-attribute/column in the base-class. But when I run my tests, I always get an error telling me that Customer has no @Id?

First I thought the problem lies in the visibility of the id-attribute, because it was private first. But even after I changed it to protected (so the subclass has direct access) it isnt working.

Person:

@Entity @Table(name="Persons") @Inheritance(strategy = InheritanceType.JOINED) @DiscriminatorColumn(name = "TYPE") public class Person {      @Id     @GeneratedValue     protected int id;     @Column(nullable = false)     protected String firstName;     @Column(nullable = false)     protected String lastName; 

Customer:

@Entity @Table(name = "Customers") @DiscriminatorValue("C") public class Customer extends Person {      //no id needed here 

I am running out of ideas and resources to look at. It should be a rather simple problem, but I just dont see it.

Answer 1

I solved it myself by creating a MappedSuperclass

@MappedSuperclass public abstract class EntityBase{    @Id    @GeneratedValue    private int id;     ...setter/getter } 

All entities are inheriting from this class. I am still wondering why the tutorials dont mention this, but maybe it gets better with the JPA 2 implementations.