The mapping of java.util.Map can be customized by using one or more of the followings annotations on the map field/property:
@CollectionTable: To customize the map table (the the foreign key table containing map's key/value columns).
@MapKeyColumn: To customize the 'key' column in the map table.
@Column: To customize the 'value' column in the map table.
Example
@Entity
public class Customer {
@Id
@GeneratedValue
private int id;
private String name;
@ElementCollection
@MapKeyColumn(name = "item")
@Column(name = "qty")
@CollectionTable(name = "ITEM_QTY")
private Map<String, Integer> itemQtyMap;
.............
}
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 ITEM_QTY");
emf.close();
} finally {
emf.close();
}
}
.............
} Output'SHOW TABLES' [CUSTOMER, PUBLIC] [ITEM_QTY, PUBLIC] 'SHOW COLUMNS from Customer' [ID, INTEGER(10), NO, PRI, NULL] [NAME, VARCHAR(255), YES, , NULL] 'SHOW COLUMNS from ITEM_QTY' [CUSTOMER_ID, INTEGER(10), NO, PRI, NULL] [QTY, INTEGER(10), YES, , NULL] [ITEM, VARCHAR(255), NO, PRI, 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");
Map<String, Integer> itemPurchased = new HashMap<>();
itemPurchased.put("XYZ Blender", 1);
itemPurchased.put("ZZZ Beer Glass", 4);
c1.setItemQtyMap(itemPurchased);
System.out.println(c1);
Customer c2 = new Customer();
c2.setName("Morgan Philips");
Map<String, Integer> orderMap2 = new HashMap<>();
orderMap2.put("AA Glass Cleaner",3);
c2.setItemQtyMap(orderMap2);
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 ITEM_QTY");
}
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', itemQtyMap={XYZ Blender=1, ZZZ Beer Glass=4}} Customer{id=0, name='Morgan Philips', itemQtyMap={AA Glass Cleaner=3}} -- Native queries -- 'Select * from Customer' [1, Lindsey Craft] [2, Morgan Philips] 'Select * from ITEM_QTY' [1, 1, XYZ Blender] [1, 4, ZZZ Beer Glass] [2, 3, AA Glass Cleaner] -- Loading Customer -- Customer{id=1, name='Lindsey Craft', itemQtyMap={XYZ Blender=1, ZZZ Beer Glass=4}} Customer{id=2, name='Morgan Philips', itemQtyMap={AA Glass Cleaner=3}}
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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