Example
Entities
@Entity
public class Employee {
@Id
@GeneratedValue
private long id;
private String name;
@ElementCollection
@OrderBy//order by strings
private List<String> phoneNumbers;
@ManyToMany(cascade = CascadeType.ALL)
@OrderBy("supervisor")//order by task.supervisor (employee.id)
private List<Task> tasks;
@ElementCollection
@OrderBy("city.country DESC")//desc order by address.city.country
private List<Address> addresses;
.............
}
@Entity
public class Task {
@Id
@GeneratedValue
private long id;
private String name;
@OneToOne
private Employee supervisor;
.............
}
@Embeddable
public class Address {
private String street;
@Embedded
private City city;
.............
}
@Embeddable
public class City {
private String name;
private String country;
.............
}
Table mappings
Let's see our entities are mapped to what database tables:
public class TableMappingMain {
private static EntityManagerFactory entityManagerFactory =
Persistence.createEntityManagerFactory("example-unit");
public static void main(String[] args) {
try {
nativeQuery("SHOW TABLES");
nativeQuery("SHOW COLUMNS FROM EMPLOYEE");
nativeQuery("SHOW COLUMNS FROM EMPLOYEE_PHONENUMBERS");
nativeQuery("SHOW COLUMNS FROM EMPLOYEE_TASK");
nativeQuery("SHOW COLUMNS FROM TASK");
nativeQuery("SHOW COLUMNS FROM EMPLOYEE_ADDRESSES");
} finally {
entityManagerFactory.close();
}
}
public static void nativeQuery(String s) {
EntityManager em = entityManagerFactory.createEntityManager();
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);
}
}
em.close();
}
}
'SHOW TABLES'
[EMPLOYEE, PUBLIC]
[EMPLOYEE_ADDRESSES, PUBLIC]
[EMPLOYEE_PHONENUMBERS, PUBLIC]
[EMPLOYEE_TASK, PUBLIC]
[TASK, PUBLIC]
'SHOW COLUMNS FROM EMPLOYEE'
[ID, BIGINT(19), NO, PRI, NULL]
[NAME, VARCHAR(255), YES, , NULL]
'SHOW COLUMNS FROM EMPLOYEE_PHONENUMBERS'
[EMPLOYEE_ID, BIGINT(19), NO, , NULL]
[PHONENUMBERS, VARCHAR(255), YES, , NULL]
'SHOW COLUMNS FROM EMPLOYEE_TASK'
[EMPLOYEE_ID, BIGINT(19), NO, , NULL]
[TASKS_ID, BIGINT(19), NO, , NULL]
'SHOW COLUMNS FROM TASK'
[ID, BIGINT(19), NO, PRI, NULL]
[NAME, VARCHAR(255), YES, , NULL]
[SUPERVISOR_ID, BIGINT(19), YES, , NULL]
'SHOW COLUMNS FROM EMPLOYEE_ADDRESSES'
[EMPLOYEE_ID, BIGINT(19), NO, , NULL]
[COUNTRY, VARCHAR(255), YES, , NULL]
[NAME, VARCHAR(255), YES, , NULL]
[STREET, VARCHAR(255), YES, , NULL]
H2 database SHOW statements
Retrieval of collections
public class ExampleMain {
private static EntityManagerFactory entityManagerFactory =
Persistence.createEntityManagerFactory("example-unit");
public static void main(String[] args) {
try {
persistEmployees();
findEmployees();
} finally {
entityManagerFactory.close();
}
}
public static void persistEmployees() {
Task task1 = Task.create("Development");
Task task2 = Task.create("Documentation");
Task task3 = Task.create("Designing");
Task task5 = Task.create("Refactoring");
Task task6 = Task.create("Testing");
Employee employee1 = Employee.create("Diana", Arrays.asList(task1, task2, task6),
Arrays.asList(Address.create("111 Round Drive", "Papineau", "Sundland"),
Address.create("2623 Elmwood Avenue", "Scottsdale", "Zwonga")),
"111-111-111", "666-666-666", "222-222-222");
Employee employee2 = Employee.create("Denise", Arrays.asList(task2, task3),
Arrays.asList(Address.create("23 Estate Avenue", "Papineau", "Ugrela"),
Address.create("367 Rose Route", "Scottsdale", "Mreyton")),
"444-444-444", "333-333-333");
Employee employee3 = Employee.create("Linda", Arrays.asList(task1, task5),
Arrays.asList(Address.create("345 Little Way", "Fries", "Tospus"),
Address.create("91 Vine Lane", "Binesville", "Oblijan")),
"555-555-555");
EntityManager em = entityManagerFactory.createEntityManager();
task1.setSupervisor(employee2);
task2.setSupervisor(employee1);
task3.setSupervisor(employee3);
task5.setSupervisor(employee1);
task6.setSupervisor(employee3);
em.getTransaction().begin();
em.persist(employee1);
em.persist(employee2);
em.persist(employee3);
em.getTransaction().commit();
}
private static void findEmployees() {
EntityManager em = entityManagerFactory.createEntityManager();
List<Employee> employees = em.createQuery("Select e from Employee e")
.getResultList();
for (Employee employee : employees) {
System.out.println("---");
System.out.println(employee);
System.out.println("-- Tasks --");
for (Task task : employee.getTasks()) {
System.out.println("task: " + task);
System.out.println("supervisor: " + task.getSupervisor());
}
System.out.println("-- addresses --");
employee.getAddresses().forEach(System.out::println);
}
}
}
---
Employee{id=1, name='Diana', phoneNumbers=[111-111-111, 222-222-222, 666-666-666]}
-- Tasks --
task: Task{id=3, name='Documentation'}
supervisor: Employee{id=1, name='Diana', phoneNumbers=[111-111-111, 222-222-222, 666-666-666]}
task: Task{id=2, name='Development'}
supervisor: Employee{id=5, name='Denise', phoneNumbers=[333-333-333, 444-444-444]}
task: Task{id=4, name='Testing'}
supervisor: Employee{id=7, name='Linda', phoneNumbers=[555-555-555]}
-- addresses --
Address{street='2623 Elmwood Avenue', city=City{name='Scottsdale', country='Zwonga'}}
Address{street='111 Round Drive', city=City{name='Papineau', country='Sundland'}}
---
Employee{id=5, name='Denise', phoneNumbers=[333-333-333, 444-444-444]}
-- Tasks --
task: Task{id=3, name='Documentation'}
supervisor: Employee{id=1, name='Diana', phoneNumbers=[111-111-111, 222-222-222, 666-666-666]}
task: Task{id=6, name='Designing'}
supervisor: Employee{id=7, name='Linda', phoneNumbers=[555-555-555]}
-- addresses --
Address{street='23 Estate Avenue', city=City{name='Papineau', country='Ugrela'}}
Address{street='367 Rose Route', city=City{name='Scottsdale', country='Mreyton'}}
---
Employee{id=7, name='Linda', phoneNumbers=[555-555-555]}
-- Tasks --
task: Task{id=8, name='Refactoring'}
supervisor: Employee{id=1, name='Diana', phoneNumbers=[111-111-111, 222-222-222, 666-666-666]}
task: Task{id=2, name='Development'}
supervisor: Employee{id=5, name='Denise', phoneNumbers=[333-333-333, 444-444-444]}
-- addresses --
Address{street='345 Little Way', city=City{name='Fries', country='Tospus'}}
Address{street='91 Vine Lane', city=City{name='Binesville', country='Oblijan'}}
As seen above:
Each employee's phoneNumbers collection elements are arranged in their natural ordering.
Each employee's tasks collection elements are arranged by supervisor's ids.
Each employee's addresses collection elements are arranged in descending order by the country names.
Example Project
Dependencies and Technologies Used:
- h2 1.4.197: H2 Database Engine.
- hibernate-core 5.2.13.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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