An embeddable class may include another embeddable class. Let's see that with an example.
Example
@Embeddable
public class ClassA {
private String myStr;
private int myInt;
.............
}
@Embeddable
public class ClassB {
private String myStrB;
@Embedded
private ClassA classARef;
.............
}
@Entity
public class MyEntity {
@Id
@GeneratedValue
private int id;
@Embedded
private ClassB classBRef;
.............
}
public class ExampleMain {
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("example-unit");
try {
EntityManager em = emf.createEntityManager();
nativeQuery(em, "SHOW TABLES");
nativeQuery(em, "SHOW COLUMNS from MyEntity");
emf.close();
} finally {
emf.close();
}
}
public static void nativeQuery(EntityManager em, String s) {
System.out.printf("-----------------------------%n'%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' [MYENTITY, PUBLIC] ----------------------------- 'SHOW COLUMNS from MyEntity' [ID, INTEGER(10), NO, PRI, NULL] [MYINT, INTEGER(10), NO, , NULL] [MYSTR, VARCHAR(255), YES, , NULL] [MYSTRB, VARCHAR(255), YES, , NULL]
Persisting and loading data
public class ExampleMain2 {
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("example-unit");
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();
ClassA a = new ClassA();
a.setMyInt(10);
a.setMyStr("a test String");
ClassB b = new ClassB();
b.setMyStrB("a test string in ClassB");
b.setClassARef(a);
MyEntity entityB = new MyEntity();
entityB.setClassBRef(b);
System.out.println(entityB);
em.getTransaction().begin();
em.persist(entityB);
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 MyEntity");
}
private static void loadEntity(EntityManagerFactory emf) {
System.out.println("-- Loading MyEntity --");
EntityManager em = emf.createEntityManager();
List<MyEntity> entityList = em.createQuery("Select t from MyEntity t")
.getResultList();
entityList.forEach(System.out::println);
em.close();
}
} Output-- Persisting entities -- EntityB{id=0, classBRef=ClassB{myStrB='a test string in ClassB', classARef=ClassA{myStr='a test String', myInt=10}}} -- native queries -- ----------------------------- 'Select * from MyEntity' [1, 10, a test String, a test string in ClassB] -- Loading MyEntity -- EntityB{id=1, classBRef=ClassB{myStrB='a test string in ClassB', 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
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