2.4.4. Inheritance

SINGLE_TABLE is a very powerful strategy but sometimes, and especially for legacy systems, you cannot add an additional discriminator column. For that purpose Hibernate has introduced the notion of discriminator formula: @DiscriminatorFormula is a replacement of @DiscriminatorColumn and use a SQL fragment as a formula for discriminator resolution (no need to have a dedicated column).

@Entity
@DiscriminatorFormula("case when forest_type is null then 0 else forest_type end")
public class Forest { ... }

By default, when querying the top entities, Hibernate does not put a restriction clause on the discriminator column. This can be inconvenient if this column contains values not mapped in your hierarchy (through @DiscriminatorValue). To work around that you can use @ForceDiscriminator (at the class level, next to @DiscriminatorColumn). Hibernate will then list the available values when loading the entities.

You can define the foreign key name generated by Hibernate for subclass tables in the JOINED inheritance strategy.

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class File { ... }

@Entity
@ForeignKey(name = "FK_DOCU_FILE")
public class Document extends File {

The foreign key from the Document table to the File table will be named FK_DOCU_FILE.