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Create a Java project "de.vogella.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 "de.vogella.jpa.eclipselink.model" and the following classes.
package de.vogella.jpa.eclipselink.model;
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;
}
}
package de.vogella.jpa.eclipselink.model;
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;
}
}
package de.vogella.jpa.eclipselink.model;
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>de.vogella.jpa.eclipselink.model.Person</class> <class>de.vogella.jpa.eclipselink.model.Family</class> <class>de.vogella.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. For details please see See JUnit Tutorial . 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.
package de.vogella.jpa.eclipselink.main;
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 de.vogella.jpa.eclipselink.model.Family;
import de.vogella.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();
}
}
The project should now look like the following.
You should be able to run the JUnit tests successfully .