- An entity may have references of other non-entity classes. Such non-entity classes are called embeddable classes.
- All fields of an embeddable class are mapped to the owner entity table.
@Embeddable annotation is used on the non-entity class. This is the class which is to be embedded in an entity class. @Embedded is used in the entity class. This annotation is placed on the field/property referring to the embeddable class.- Embedded objects belong strictly to their owning entity, and should not be shared across persistent entities.
- Embeddable class and it's fields/properties can use all annotations used by an entity (e.g. @Column etc), except for the @Entity annotation.
Example
@Entity
public class EntityA {
@Id
@GeneratedValue
private int id;
@Embedded
private ClassA classARef;
.............
}
@Embeddable
public class ClassA {
private String myStr;
private int myInt;
.............
}
public class ExampleMain {
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("test");
try {
EntityManager em = emf.createEntityManager();
nativeQuery(em, "SHOW TABLES");
nativeQuery(em, "SHOW COLUMNS from EntityA");
emf.close();
} finally {
emf.close();
}
}
public static void nativeQuery(EntityManager em, String s) {
System.out.printf("'%s'%n", s);
Query query = em.createNativeQuery(s);
List list = query.getResultList();
for (Object o : list) {
if(o instanceof Object[]) {
System.out.println(Arrays.toString((Object[]) o));
}else{
System.out.println(o);
}
}
}
}Output'SHOW TABLES'
[ENTITYA, PUBLIC]
'SHOW COLUMNS from EntityA'
[ID, INTEGER(10), NO, PRI, NULL]
[MYINT, INTEGER(10), NO, , NULL]
[MYSTR, VARCHAR(255), YES, , NULL]
H2 database SHOW statements
A quick overview of the example:
Persisting and loading data
public class ExampleMain2 {
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("test");
try {
persistEntity(emf);
runNativeQueries(emf);
loadEntity(emf);
} finally {
emf.close();
}
}
private static void persistEntity(EntityManagerFactory emf) {
System.out.println("-- Persisting entities --");
EntityManager em = emf.createEntityManager();
EntityA entityA = new EntityA();
ClassA a = new ClassA();
a.setMyInt(10);
a.setMyStr("a test String");
entityA.setClassARef(a);
System.out.println(entityA);
em.getTransaction().begin();
em.persist(entityA);
em.getTransaction().commit();
em.close();
}
private static void runNativeQueries(EntityManagerFactory emf) {
System.out.println("-- native queries --");
EntityManager em = emf.createEntityManager();
ExampleMain.nativeQuery(em, "Select * from EntityA");
}
private static void loadEntity(EntityManagerFactory emf) {
System.out.println("-- Loading EntityA --");
EntityManager em = emf.createEntityManager();
List<EntityA> entityAList = em.createQuery("Select t from EntityA t")
.getResultList();
entityAList.forEach(System.out::println);
em.close();
}
}Output-- Persisting entities --
EntityA{id=0, classARef=ClassA{myStr='a test String', myInt=10}}
-- native queries --
'Select * from EntityA'
[1, 10, a test String]
-- Loading EntityA --
EntityA{id=1, classARef=ClassA{myStr='a test String', myInt=10}}
Example ProjectDependencies and Technologies Used: - h2 1.4.193: H2 Database Engine.
- hibernate-core 5.2.8.Final: The core O/RM functionality as provided by Hibernate.
Implements javax.persistence:javax.persistence-api version 2.1 - JDK 1.8
- Maven 3.3.9
|
|
