inheritance in openjpa

Put this annotation on the super class.
@Inheritance(strategy = InheritanceType.JOINED)

The option here is

• SINGLE_TABLE
• TABLE_PER_CLASS
• JOINED

SINGLE_TABLE


TABLE_PER_CLASS


JOINED


To persist animal:

em.persist(new Animal(1,"honey"));

Openjpa will generate the sql below

INSERT INTO Animal (id, name) VALUES (1, 'honey')

To persist fish:

em.persist(new Fish(2,"mermaid","SEA"));

Openjpa will generate the sql below

INSERT INTO Animal (id, name) VALUES (2, 'mermaid')
INSERT INTO Fish (id, territory) VALUES (2, 'SEA')

To query animal:

em2.createQuery("select m from Animal m").getResultList();

Openjpa will generate the sql below

SELECT t0.id, t1.id, t2.id, t0.name, t1.sex, t2.territory 
FROM Animal t0 
LEFT OUTER JOIN Dog t1 ON t0.id = t1.id 
LEFT OUTER JOIN Fish t2 ON t0.id = t2.id 

Openjpa will map the result to Fish or Dog object automatically.

To query fish:

em2.createQuery("select fish from Fish fish").getResultList();

Openjpa will generate the sql below

SELECT t1.id, t0.id, t1.name, t0.territory 
FROM Fish t0 
INNER JOIN Animal t1 ON t0.id = t1.id

Openjpa will map the the result to Fish object.