Hibernate + Inheritance

Question

I’ve been trying for some time a solution to my problem. I’ve done a lot of research but nothing clearly explains what I need.

So I created an example application and am making it available from this link: Application

To run this application simply use the Netbeans IDE and create a Mysql DB with the following name: "testHeranca".

My question is this::

I have two entities, Participant and Issuer. Issuer class extends the participating class. For example:

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@Table(name = "participante")
public class Participante implements Serializable{

    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Long id;
    @Column(name = "nome", nullable = false, length = 100)
    private String nome;
    @Column(name = "documento", nullable = false, length = 100)
    private String documento;
    ...
}



@Entity
@Table(name = "emitente")
@PrimaryKeyJoinColumn(name = "id")
public class Emitente extends Participante{

    @Column(name = "cargo", nullable = false, length = 100)
    private String cargo;
    ...
}

Suppose I have a participant already registered in my database, if I want to register a new issuer from this existing participant, how should I proceed? Does Hibernate do this for me? With the test I passed in the example this does not happen.

Answer 1

Although I don’t know all the details of Hibernate and other JPA implementations, because each one has its particularities, I don’t think it is possible to include part of a legacy relationship.

Thinking that JPA works with a limited kind of polymorphism, this would be like changing the type of the object.

In that particular situation, a viable alternative would be to change the type of inheritance relationship to aggregation, i.e., where Emitente has an attribute of the type Participante. This way the tables do not need to be changed and you can include separate entities at any time.

Other alternatives exist, as already mentioned in Anthony Accioly’s comment:

1. Include issuer via JDBC or Native Query and then read via JPA
2. Remove the participant and re-include it as an issuer