How to not reinialize tables created with JPA?

[Siegfried Heintze]

This example seems to work: http://javahowto.blogspot.com/2006/07/helloworld-with-jpa-toplink-and-mysql.html

However, when I comment out the statements that create and delete the objects (as I have done below), I expect to see it display the same greetings and messages. Instead, no messages are being retrieved. Apparently something is recreating the database tables every time I run the program. What do change so I can run this program and see the data previously entered into the database?

Thanks,
Siegfried

HelloWorld.java:

package com.foo;
import java.util.List;
 
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;
 
public class HelloWorld {
 private EntityManagerFactory emf;
 private EntityManager em;
 private String PERSISTENCE_UNIT_NAME = "hello-world";
 
 public static void main(String[] args) {
     HelloWorld hello = new HelloWorld();
     hello.initEntityManager();
//     hello.create();
     hello.readAll();
//     hello.deleteAll();
//     hello.readAll();
//     hello.create();
//     hello.readAll();
     hello.closeEntityManager();
 }
 
 private void initEntityManager() {
     emf = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
     em = emf.createEntityManager();
 }
 
 private void closeEntityManager() {
     em.close();
     emf.close();
 }
 
 private void create() {
     em.getTransaction().begin();
     Greeting g_en = new Greeting("hello world", "en");
     Greeting g_es = new Greeting("hola, mundo", "es");
     Greeting[] greetings = new Greeting[]{g_en, g_es, 
     new com.foo.Message("hello", "en", "siegfried", "judy"),
     new Message("hallo", "de", "siegfried", "tally")};
     for(Greeting g : greetings) {
         em.persist(g);
     }
     em.getTransaction().commit();
 }
 
 private void read() {
     Greeting g = (Greeting) em.createQuery(
             "select g from Greeting g where g.language = :language")
             .setParameter("language", "en").getSingleResult();
     System.out.println("Query returned: " + g);
 }
 private void readAll() {
     List<Greeting> greets = em.createQuery(
             "select g from Greeting g").getResultList();
     System.out.println("Found "+greets.size()+" greetings");
     for(Greeting greet : greets)
     System.out.println("Query returned: " + greet);
 }
 private void deleteAll() {
     Query q = em.createQuery("delete from Greeting g");
     q.executeUpdate();
 }
}

Greeting.java:

package com.foo;
import java.io.Serializable;
import javax.persistence.Basic;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
 
@SuppressWarnings("serial")
@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class Greeting implements Serializable {
private static final long serialVersionUID = 833700959862290788L;
@Id @GeneratedValue private int id;
 @Basic private String message;
 @Basic private String language;
 
 public Greeting() {}
 public Greeting(String message, String language) {
     this.message = message;
     this.language = language;
 }
 
 public String toString() {
     return "Greeting id=" + id + ", message=" + message + ", language=" + language;
 }
}

Message.java:

package com.foo;
public class Message extends Greeting {
public Message() {
}
public Message(String message, String language, String src, String dst) {
super(message, language);
    this.src = src;
    this.dst = dst;
 }
  public String src, dst;
  public String toString() {
     return super.toString()+" src="+src + " dst="+dst;
 }
}
 

[Vesa Tanhua-Tyrkk�]

Hi,

This is configured in persistence.xml by property:
<property name="toplink.ddl-generation" value="drop-and-create-tables"/>

possible values for this are create-tables, drop-and-create-tables,none

So I think that by removing that property form persistence.xml preserves your data.