Transient members

[zauberlehrling]

Hello,

I have a question concerning transient members. In the follwoing code there is an Entity Bean:

package entities;

import java.io.Serializable;
import java.util.*;
import javax.persistence.*;

@Entity
public class Node implements Serializable {

 private int id;
 private String persistentText;
 private String transientText;

 public Node(){}

 public Node(int id)
 {
 setId(id);
 }

 @Id
 public int getId() {
 return id;
 }

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

 public String getPersistentText() {
 return persistentText;
 }

 public void setPersistentText(String persistentText) {
 this.persistentText = persistentText;
 }

 @Transient
 public String getTransientText() {
 return transientText;
 }

 public void setTransientText(String transientText) {
 this.transientText = transientText;
 }
}

a Session Bean:

package server.sessions;

import javax.ejb.*;
import javax.persistence.*;
import org.hibernate.*;
import entities.*;

import java.util.*;

@Stateful
public class ClientSessionBean implements ClientSessionLocal, ClientSessionRemote{

 @PersistenceContext private EntityManager manager;

 List<Node> nodes;
 Node node;

 public void createNode()
 {
 node = new Node(1);
 node.setTransientText("transient");
 node.setPersistentText("persistent");
 manager.persist(node);
 nodes = manager.createQuery("from Node where id=1").getResultList();
 node = nodes.get(0);
 System.out.println("createNode persistentText: "+node.getPersistentText());
 System.out.println("createNode transientText: "+node.getTransientText());
 }

 public void showNode()
 {
 nodes = manager.createQuery("from Node where id=1").getResultList();
 node = nodes.get(0);
 System.out.println("showNode persistentText: "+node.getPersistentText());
 System.out.println("showNode transientText: "+node.getTransientText());
 }

}

and a client, which calls the two methods createNode() and showNode():

package client;

import javax.naming.InitialContext;
import java.util.*;
import entities.*;
import server.sessions.*;

public class Client {

 static ClientSession clientSession;

 public static void main(String[] args) {
 try {
 Hashtable<String,String> env = new Hashtable<String,String>();
 env.put("java.naming.factory.initial", "org.jnp.interfaces.NamingContextFactory");
 env.put("java.naming.factory.url.pkgs", "org.jboss.naming:org.jnp.interfaces");
 env.put("java.naming.provider.url", "localhost");
 InitialContext ctx = new InitialContext(env);
 clientSession = (ClientSession)ctx.lookup("ClientSessionBean/remote");
 clientSession.createNode();
 clientSession.showNode();
 }
 catch (Exception e)
 {
 System.out.println(e);
 }
 }
}

I get the following answer:
..
10:59:02,531 INFO [STDOUT] createNode persistentText: persistent
10:59:02,531 INFO [STDOUT] createNode transientText: transient
10:59:02,562 INFO [STDOUT] showNode persistentText: persistent
10:59:02,562 INFO [STDOUT] showNode transientText: null
..
Is the last line correct? I've exptected the last line:

10:59:02,562 INFO [STDOUT] showNode transientText: transient

Thanks for your efforts.

[mwoelke]

of course its correct.
The spec says:

9.1.14 Transient Annotation
The Transient annotation is used to annotate a property or field of the entity class. It specifies that
the property or field is not persistent.
@Target({METHOD, FIELD}) @Retention(RUNTIME)
public @interface Transient {}
Example:
@Entity
public class Employee {
@Id int id;
@Transient User currentUser;
...
}

which means, that if u fetch a entity bean from the database, its transient members can not be initialized since they are not stored.

regards, milan wölke

[zauberlehrling]

Hello Milan,

thanks for your answer.
Do you know wether the entity bean is always fetched
from the database or is it possible that the entity bean exist
as an object in the java virtual machine? Of course changes
to the persistent fields must be in sync with the database.

Best Regards

Frank

[mwoelke]

U r referring to some kind of caching, dont u.
Unfortunately a cache is not part of the ejb30 spec, but u can use the hibernate l2 cache. It keeps your entitybeans in memory, and keeps them in sync with the db. the drawback is, that u have to use hibernate annotations with your entity beans, which i personally dislike.

--> hint: jboss-entity-cache

dont ask me, is transient field would survive caching, u have to try that.

but to answer the first question, if u dont use l2 caching, yes it will be fetched every time.

[zauberlehrling]

Although the data is not persistent via the EJB3 persistence mechanism, I would like to keep some data in the entity beans.
I will take a closer look at the the jboss-entity-cache!

[zauberlehrling]

Hello Milan,

thank you for your hint. I switched on the EJB3EntityTreeCache and this cache works. One can check this via

jmx-console
-> service=EJB3EntityTreeCache
-> java.lang.String printDetails() invoke

But here is a catch in it! Only the data persistent via the hibernate mapping is cached. So this does not have the desired effect.

I'm trying now the following: I create a reference from the JNDI to this bean. If I access the field transientText in the Node-bean, then I get the originally value.