Re: EJB, EntityManager and merging problems

pmz <>
Tue, 3 Aug 2010 05:29:02 -0700 (PDT)
On 3 Sie, 13:47, pmz <> wrote:

On 2 Sie, 21:31, Arved Sandstrom <> wrote:

Przemek M. Zawada wrote:


I've been looking for nice database I/O way and I've decided to use
(suggested by NetBeans) the EJB.

In fact, I was looking for something, which would speed up my work,
unfortunately I'm stuck for last 4 hours with annoying update databas=



Fetching data from database works perfectly. BUT, when I'm trying to
update records, I no changes are made in the database. I wish you'll
help me finding the reason.

As it has been described in many, many google-found pages, I've build=


object, which I use as entity manager. Sample:

public class UserManager {

    private EntityManager em;
    SessionContext context;
    private CupUserFacade userFacade; // Dunno whether it's requi=


    public int UpdateUser() {
        EntityManagerFactory emf =

        em = emf.createEntityManager();
        CupUser user = (CupUser) em.find(CupUser.class, 2);
    user.setName("fonk you");
        try {
            CupUser upUser = em.merge(user);

            return 1;
        } catch (Exception ex) {
        "UserManager.UpdateUser(): "
            + ex.getMessage());
            return 0;


    public void setEntityManager(EntityManager eman) {
        this.em = eman;

The log file sayz:

FINEST: Execute query ReadObjectQuery(referenceClass=CupUser sql==


... FROM cup_user WHERE (ID = ?)")
SEVERE: fonk you
FINEST: Merge clone with references entity.CupUser[id=2]
SEVERE: true // is open() EntityManager
FINER: release unit of work

In fact it does not say anything about updating queries...
That's annoying, because I really don't know what am I doing wrong.

Please help. Thank you very much.

Przemek M. Zawada

Hi, Przemek

You've got a bit too much going on here at one. For starters, decide
whether you are going to use @PersistenceUnit *or* @PersistenceContext
*or* Persistence.createEntityManagerFactory().createEntityManager() to
obtain your entity managers. Container-managed will be one of the first
2 choices; application-managed is the third.

I strongly recommend reading


As an aside, note that inside a transactional boundary em.find() will
returned a managed entity - there is no need to then merge it. Again, I
recommend that you read the above link; however, depending on your
scenario either the container will take care of transactions for you
(with container-managed EMs), or you will, by either using the
EntityTransaction or UserTransaction APIs. In this case you had an
application-managed EM but no transaction...hence no update.


Give a man a fish, and he can eat for a day. But teach a man how to
fish, and he'll be dead of mercury poisoning inside of three years.
--Charles Haas

Thank you for your time! Yeah, I've discovered that I've mixed all of
everything, very stupid. I've been instructed to try such solution:

public class UserManager {
@PersistenceContext(unitName = "RallySuitePU")
private EntityManager em;
void Update() {
  System.err.println("em.find() start");
  CupUser user = (CupUser) em.find(CupUser.class, 2); /// Crashed her=


with NullPointerException, of course
  user.setUserName("New Username Here");


Obviously my em is NullPointer - why it has not been initialized? Or
how should I do it?

All the best,
Przemek M. Zawada

Okay, I've managed where the problem is. I'm not sure whether it's
allowed to do (what I've done) in servlet part, but for tests I've
allowed myself to do it.

I've add in the servlet elements:
@PersistenceContext(unitName = "RallySuitePU")
private EntityManager em;

UserTransaction ut;

and in the doPost section, I've made such test:

CupUser u = (CupUser) em.find(CupUser.class,

The row has been updated (in the database), with such log message:

FINER: TX binding to tx mgr, status=STATUS_ACTIVE
FINEST: Execute query ReadObjectQuery(referenceClass=CupUser
sql="SELECT ID, IsActive, User_IsLocked, User_Contact, User_Mobile,
User_Password, User_Name, User_ReminderCode, User_Email,
User_FullName, User_LastLogin, User_Type FROM cup_user WHERE (ID
= ?)")
FINER: TX beforeCompletion callback, status=STATUS_ACTIVE
FINER: begin unit of work commit
FINER: TX afterCompletion callback, status=COMMITTED
FINER: end unit of work commit
FINER: release unit of work
FINER: client released

Unfortunately, I have some problems with data preview - in the browse
page I have the old data (e-mail value is i.e. old_value) but when I
view it as another page (edit-mode), the e-mail value is valid, new
one "fonkyou". About what I'm missing? Any refresh/reload/etc.

All the best,
Przemek M. Zawada

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