JPA : Relationship Example using eclipse link

Create a Java project "com.vaani.jpa.eclipselink", create again a folder "lib" and place the required JPA jars and derby.jar into this folder. Add the libs to the project classpath.
Create the package "com.vaani.jpa.eclipselink.model" and the following classes.

import java.util.ArrayList;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
public class Family {
@Id
@GeneratedValue(strategy = GenerationType.TABLE)
private int id;
private String description;

@OneToMany(mappedBy = "family")
private final List<Person> members = new ArrayList<Person>();

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getDescription() {
return description;
}

public void setDescription(String description) {
this.description = description;
}

public List<Person> getMembers() {
return members;
}

}

import java.util.ArrayList;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Transient;

@Entity
public class Person {
@Id
@GeneratedValue(strategy = GenerationType.TABLE)
private String id;
private String firstName;
private String lastName;

private Family family;

private String nonsenseField = "";

private List<Job> jobList = new ArrayList<Job>();

public String getId() {
return id;
}

public void setId(String Id) {
this.id = Id;
}

public String getFirstName() {
return firstName;
}

public void setFirstName(String firstName) {
this.firstName = firstName;
}

// Leave the standard column name of the table
public String getLastName() {
return lastName;
}

public void setLastName(String lastName) {
this.lastName = lastName;
}

@ManyToOne
public Family getFamily() {
return family;
}

public void setFamily(Family family) {
this.family = family;
}

@Transient
public String getNonsenseField() {
return nonsenseField;
}

public void setNonsenseField(String nonsenseField) {
this.nonsenseField = nonsenseField;
}

@OneToMany
public List<Job> getJobList() {
return this.jobList;
}

public void setJobList(List<Job> nickName) {
this.jobList = nickName;
}

}

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Job {
@Id
@GeneratedValue(strategy = GenerationType.TABLE)
private int id;
private double salery;
private String jobDescr;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public double getSalery() {
return salery;
}

public void setSalery(double salery) {
this.salery = salery;
}

public String getJobDescr() {
return jobDescr;
}

public void setJobDescr(String jobDescr) {
this.jobDescr = jobDescr;
}

}

Create the file "persistence.xml" in "src/META-INF". Remember to change the path to the database.

<?xml version="1.0" encoding="UTF-8" ?>
<persistence xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0" xmlns="http://java.sun.com/xml/ns/persistence">
<persistence-unit name="people" transaction-type="RESOURCE_LOCAL">


<class>com.vaani.jpa.eclipselink.model.Person</class>
<class>com.vaani.jpa.eclipselink.model.Family</class><class>com.vaani.jpa.eclipselink.model.Job</class>
<properties>
<property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.EmbeddedDriver" />
<property name="javax.persistence.jdbc.url"
value="jdbc:derby:/home/vogella/databases/relationsshipDb;create=true" />
<property name="javax.persistence.jdbc.user" value="test" />
<property name="javax.persistence.jdbc.password" value="test" />

<!-- EclipseLink should create the database schema automatically -->
<property name="eclipselink.ddl-generation" value="create-tables" />
<property name="eclipselink.ddl-generation.output-mode"
value="database" />
</properties>

</persistence-unit>
</persistence>

The following check is implemented as a JUnit Test. The setup() method will create a few test entries. After the test entries are created, they will be read and the one field of the entries is changed and saved to the database.

import static org.junit.Assert.assertTrue;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;

import org.junit.Before;
import org.junit.Test;

import com.vaani.jpa.eclipselink.model.Family;
import com.vaani.jpa.eclipselink.model.Person;

public class JpaTest {

private static final String PERSISTENCE_UNIT_NAME = "people";
private EntityManagerFactory factory;

@Before
public void setUp() throws Exception {
factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
EntityManager em = factory.createEntityManager();

// Begin a new local transaction so that we can persist a new entity
em.getTransaction().begin();

// Read the existing entries
Query q = em.createQuery("select m from Person m");
// Persons should be empty

// Do we have entries?
boolean createNewEntries = (q.getResultList().size() == 0);

// No, so lets create new entries
if (createNewEntries) {
assertTrue(q.getResultList().size() == 0);
Family family = new Family();
family.setDescription("Family for the Knopfs");
em.persist(family);
for (int i = 0; i < 40; i++) {
Person person = new Person();
person.setFirstName("Jim_" + i);
person.setLastName("Knopf_" + i);
em.persist(person);
// First we have to persists the job
// Now persists the new person
family.getMembers().add(person);
em.persist(person);
em.persist(family);
}
}

// Commit the transaction, which will cause the entity to
// be stored in the database
em.getTransaction().commit();

// It is always good practice to close the EntityManager so that
// resources are conserved.
em.close();

}

@Test
public void checkAvailablePeople() {

// Now lets check the database and see if the created entries are there
// Create a fresh, new EntityManager
EntityManager em = factory.createEntityManager();

// Perform a simple query for all the Message entities
Query q = em.createQuery("select m from Person m");

// We should have 40 Persons in the database
assertTrue(q.getResultList().size() == 40);

em.close();
}

@Test
public void checkFamily() {
EntityManager em = factory.createEntityManager();
// Go through each of the entities and print out each of their
// messages, as well as the date on which it was created
Query q = em.createQuery("select f from Family f");

// We should have one family with 40 persons
assertTrue(q.getResultList().size() == 1);
assertTrue(((Family) q.getSingleResult()).getMembers().size() == 40);
em.close();
}

@Test(expected = javax.persistence.NoResultException.class)
public void deletePerson() {
EntityManager em = factory.createEntityManager();
// Begin a new local transaction so that we can persist a new entity
em.getTransaction().begin();
Query q = em
.createQuery("SELECT p FROM Person p WHERE p.firstName = :firstName AND p.lastName = :lastName");
q.setParameter("firstName", "Jim_1");
q.setParameter("lastName", "Knopf_!");
Person user = (Person) q.getSingleResult();
em.remove(user);
em.getTransaction().commit();
Person person = (Person) q.getSingleResult();
// Begin a new local transaction so that we can persist a new entity

em.close();
}
}