Using OpenJPA

I’ve implemented a simple example using OpenJPA as persistence system. This is my first experience using OpenJPA and I like it, I think that OpenJPA is really a great API. I hope that this post serves as aid to other people who start with OpenJPA.

I started using the “hellojpa” example and the OpenJPA User’s Guide

Writting a simple persistence class:

@Entity
public class Person {
	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	@Column(name = "id_person")
	private long idPerson;

	@Basic
	@Column(nullable = false, length = 30)
	private String name;

	@Basic
	@Column(name = "e_mail")
	private String mail;

	public Person() {}

	public String getMail() {
		return mail;
	}

	public void setMail(String mail) {
		this.mail = mail;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public long getIdPerson() {
		return idPerson;
	}

	public void setIdPerson(long idPerson) {
		this.idPerson = idPerson;
	}
}

Annotations are very intuitive and powerful.

Writting the persistence.xml I used MySQL as database.

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    version="1.0">
    <persistence-unit name="example" transaction-type="RESOURCE_LOCAL">
        <class>example.Person</class>
        <properties>
            <property name="openjpa.jdbc.SynchronizeMappings"
                value="buildSchema"/>
            <property name="openjpa.ConnectionURL"
                value="jdbc:mysql://localhost/openjpa"/>
            <property name="openjpa.ConnectionDriverName"
                value="com.mysql.jdbc.Driver"/>
            <property name="openjpa.ConnectionUserName"
                value="user"/>
            <property name="openjpa.ConnectionPassword"
                value="password"/>
        </properties>
    </persistence-unit>
</persistence>

The property “openjpa.jdbc.SynchronizeMappings” is amazing, you don’t need any sql definitions of the tables or the rows, the OpenJPA creates the tables with your object information and if you add a variable it makes an alter automatically.

And finally contructing the EntityManage and saving the object:

        EntityManagerFactory factory = Persistence.
                createEntityManagerFactory("example", System.getProperties());

        EntityManager em = factory.createEntityManager();

        em.getTransaction().begin();

        Person person = new Person();
        person.setName("Ignacio Andreu");
        person.setMail("plunchete AT gmail DOT com");
        em.persist(person);

        em.getTransaction().commit();

        em.close();

And this is all