Persist an entity that is inherited

Question

I have an entity Person which is inherited in another entity Administrator. In the bank I already have data in the entity Person and I want to associate a Person in the entity Administrator. How can I do that? Details: I am using hibernate, and using a class Dao who inherits JpaRepository

---

Class: Pessoa

@Entity
@Getter
@Setter
@Inheritance(strategy = InheritanceType.JOINED)
public class Pessoa extends PersistableEntity<Long> { // Essa herança tem o Id, e os equals&hashCode

    private static final long serialVersionUID = 1L;

    private String nome;

---

Class: Administrator

@Entity
@Getter
@Setter
public class Administrador extends Pessoa {

    private static final long serialVersionUID = 1L;

Answer 1

Possible Solution

The question code would work with some adjustments to the annotations. You might consider as if there were already entity data Administrador. If you recover one Administrador which does not have a record in the respective table, but is a Pessoa valid, Hibernate will probably generate a LEFT OUTER JOIN and recover existing data by ignoring others. So, a update would include the data in the subclass table.

Note that this is an assumption. There may be details that prevent this approach.

Problems

On the other hand, although a Administrador be a Pessoa, this modeling brings problems to the implementation. Indeed, will the Pessoa shouldn’t be a Administrador?

In any case, the heritage as implemented in Hibernate is not so flexible as to reflect any hierarchy we create in classes. On the contrary, methods are very limited.

One of the most common examples is the question of polymorphism. For example, Hibernate even allows some kind of polymorphism, but in general, common inheritance strategies like table per subclass only allow you to handle a limited set of subclasses and not directly with the superclasses.

It makes sense to use Hibernate inheritance when a superclass has several possible subclasses and not just one. In this case, it is necessary to note the superclass with @DiscriminatorColumn to inform Hibernate of a column that defines what kind of subclass each record should represent.

Ideal Solution

In your context, my indication would be not to use inheritance, but a relationship 1:1 (one-to-one) between Pessoa and Administrador. More specifically, the class Administrador could have an attribute like Pessoa. I imagine the table Administrador already have a Foreign Key for Pessoa, is not?

I know it might sound a little strange, but it makes sense if you think in terms of:

• Do not change existing code in class Pessoa
• Avoid unnecessary complexity in mapping with Hibernate
• Do not impact functionalities that use the class Pessoa, but who has no dependency on the class Administrador
• It’s simply simpler