如何在数据库中保存层次结构类？

Question

I use Java and Hibernate to save my entities in database but it's not working as needed. I have a entity Entreprise :

@Entity
public class Entreprise{

@Id
private long identifier;

@OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private List<Person>  persons;

...
// getters and setters

} 

Here the Person entity which a super class of other entities:

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public class Person{

@Id
private long identifier;

@Column
private String name;

...
 // constructors,getter and setter

} 

And my two subclasses :

@Entity
public class Employed extends Person{

 @Column
 private String actualJob;

 // constructors,getter and setter
}


@Entity
public class Unemployed extends Person{

 @Column
 private String lastJob;

// constructors,getter and setter
}

Here my method to save the entity in the database :

Person person = new Employed();
person.setName("John");
Employed employed = (Employed) person;
employed.setActualJob("electrician");
Entreprise myEntreprise = new Entreprise();
entreprise.getPersons().addPerson(person);
entrepriseDao.save(entreprise);

But in the database, the insert was just made in the table Entreprise and Person. Nothing was inserted in the table Employed. I don't know why if someone could explain me, please ?

I try the following code does not also work :

Employed employed = new Employed();
employed.setActualJob("electrician");
employed.setName("John");
Entreprise myEntreprise = new Entreprise();
entreprise.getPersons().addPerson(employed);
entrepriseDao.save(entreprise);

I don't understand why even if i use the subclass to set data it does not work.

Here is the ddl

Hibernate: insert into Entreprise_Person (Entreprise_identifier, person_identifier) values (?, ?);

Answer 1

You are adding a person reference to the enterprise´s list:

entreprise.getPersons().addPerson(person);

Doing that, you add only the person´s data, not the extended employed's data. You should add the employed object instead.

Answer 2

Try adding @PrimaryKeyJoinColumn(name = "YOUR_SUBCLASS_ID_FIELD_THAT_WILL_MATCH_THE_SUPERCLASS_ID_FIELD") to all subclasses.

The subclasses need identifiers also, this is how they link to their superclass record.

@Entity
@PrimaryKeyJoinColumn(name = "identifier")
public class Employed extends Person{

 @Id
 private long identifier;

 @Column
 private String actualJob;

 // constructors,getter and setter
}


@Entity
@PrimaryKeyJoinColumn(name = "identifier")
public class Unemployed extends Person{

 @Id
 private long identifier;

 @Column
 private String lastJob;

// constructors,getter and setter
}