JPA - Customizing @ElementCollection table attributes by using @CollectionTable

To customize foreign-key table mapped by @ElementCollection (both for basic types or embedded types), @CollectionTable can be used. This is specially useful when we already have a collection table to be mapped.

Example

@Entity
public class Customer {
    @Id
    @GeneratedValue
    private int id;
    private String name;
    @ElementCollection
    @CollectionTable(name = "PHONES", joinColumns = @JoinColumn(name = "CUST_ID"))
    @Column(name = "PH_NO")
    private List<String> phoneNumbers;
    .............
}

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 Customer");
            nativeQuery(em, "SHOW COLUMNS from Phones");
            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'
[CUSTOMER, PUBLIC]
[PHONES, PUBLIC]
'SHOW COLUMNS from Customer'
[ID, INTEGER(10), NO, PRI, NULL]
[NAME, VARCHAR(255), YES, , NULL]
'SHOW COLUMNS from Phones'
[CUST_ID, INTEGER(10), NO, , NULL]
[PH_NO, 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();

        Customer c1 = new Customer();
        c1.setName("Lindsey Craft");
        c1.setPhoneNumbers(Arrays.asList("111-111-1111", "222-222-222"));
        System.out.println(c1);

        Customer c2 = new Customer();
        c2.setName("Morgan Philips");
        c2.setPhoneNumbers(Arrays.asList("333-333-3333"));
        System.out.println(c2);

        em.getTransaction().begin();
        em.persist(c1);
        em.persist(c2);
        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 Customer");
        ExampleMain.nativeQuery(em, "Select * from Phones");
    }

    
    private static void loadEntity(EntityManagerFactory emf) {
        System.out.println("-- Loading Customer --");
        EntityManager em = emf.createEntityManager();
        List<Customer> entityAList = em.createQuery("Select t from Customer t")
                                       .getResultList();
        entityAList.forEach(System.out::println);
        em.close();
    }
}

Output

-- Persisting entities --
Customer{id=0, name='Lindsey Craft', phoneNumbers=[111-111-1111, 222-222-222]}
Customer{id=0, name='Morgan Philips', phoneNumbers=[333-333-3333]}
-- Native queries --
'Select * from Customer'
[1, Lindsey Craft]
[2, Morgan Philips]
'Select * from Phones'
[1, 111-111-1111]
[1, 222-222-222]
[2, 333-333-3333]
-- Loading Customer --
Customer{id=1, name='Lindsey Craft', phoneNumbers=[111-111-1111, 222-222-222]}
Customer{id=2, name='Morgan Philips', phoneNumbers=[333-333-3333]}

Example Project

Dependencies 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