Mapping multi-Level inheritance in Hibernate with Annotations

Question

Take the situation listed in this question:

Mapping multi-Level inheritance in Hibernate

How would this mapping be done with Annotations rather than an hbm file?

Solution

What specifically are you having trouble with? Mapping class hierarchy via joined subclasses is pretty straightforward:

@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class A implements Serializable { ... }

@Entity
public class B extends A { ... }

@Entity
@PrimaryKeyJoinColumn(name="A_ID")
public class C extends A { ... }

@Entity
@PrimaryKeyJoinColumn(name="B_ID")
public class D extends B { ... }

---

Update (based on Michal's comment).

In case you do want to use discriminators (and you should have a good reason to do so), it's possible to do so by mixing table-per-class-hierarchy strategy with secondary tables:

@Entity
@Table(name="A_table")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="entity_type")
@DiscriminatorValue("A")
public class A implements Serializable { ... }

@Entity
@SecondaryTable(name="B_table")
public class B extends A { ... }

@Entity
@SecondaryTable(name="C_table", pkJoinColumns={
    @PrimaryKeyJoinColumn(name="A_ID", referencedColumnName="ID")
))
public class C extends A { ... }

@Entity
@SecondaryTable(name="D_table", pkJoinColumns={
    @PrimaryKeyJoinColumn(name="B_ID", referencedColumnName="ID")
))
public class D extends B { ... }

The downside to this approach is you'll have to explicitly specify the table for each property mapped:

public class D extends B {
  @Column(table="D_table")
  private String someProperty;

  ...
}