JPA issue: A parent cannot be established or changed once an object has been persisted.

[Nermin]

Dear GWT developers,

I have a "probably simple" problem with my application which I am obviously not able to solve.

Two Classes: Company, Tradesman

@Entity
public class Company {
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "company")
    private List<Tradesman> users = new ArrayList<Tradesman>();

....
}


@Entity
public class Tradesman extends User{
    @ManyToOne
    private Company company;

    @PrePersist
    public void hashPassword(){
        setPassword(BCrypt.hashpw(entity.getPassword(), BCrypt.gensalt());
    }

JSR 303 validation on GWT is activated.

Here is the error message:
Detected attempt to establish Company(no-id-yet) as the parent of Tradesman(356) but the entity identified by Tradesman(356) has already been persisted without a parent.  A parent cannot be established or changed once an object has been persisted.

My problem is obviously that when I change some parameters within the Tradesman entity within the @PrePersist method, a new child entity is created.
In case I do not touch any parameter, in the @PrePersist, everything works fine.

What am I doing wrong here?

Thank you in advance:

Nermin

[Thomas Broyer]

You're not reaching the appropriate group ;-)

I suppose you're using AppEngine (form what I know of JPA, I can't see a reason for that kind of message, unless you're using JPA on AppEngine), in which case you can ask for support on StackOverflow: https://developers.google.com/appengine/community

[Juan Pablo Gardella]

Update your entity as: 

@Entity
public class Tradesman extends User{

    @ManyToOne(optional=false)

    private Company company;

    @PrePersist
    public void hashPassword(){
        setPassword(BCrypt.hashpw(entity.getPassword(), BCrypt.gensalt());
    }

And then check where are you persisting Tradesman without company. 

2013/5/21 Thomas Broyer <t.br...@gmail.com>

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[Nermin]

Dear Juan,

I tried @ManyToOne(optional=false), unfortunately no changes.
In my current setting, the @PrePersist is called only once. (I see it on system out) That means: no multiple attempts to persist Tradesman entity.

However, it looks to me that whenever I change parameters on the Tradesman entity JPA creates/persists for some reason the Tradesman in the DB, independently from the Company entity.
I use Standard GWT settings: GWT 2.5, DataNucleus on Appengine Datastore.

The scenario I am describing here is a standard scenario you will face when using GWT with JPA. I am surprised that my code is not working.
@PrePersist works fine as long as the Entity is not in a owned relation with other entities.

Does anyone has an idea what could be wrong here?

Thank you!!

Nermin

@Thomas: Thank you for the advise. I will

2013/5/21 Thomas Broyer <t.br...@gmail.com>

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[Juan Pablo Gardella]

You should persist company before persist Tradesman or attach to an existent company. This relation should be explicit. Create company.addTrademan(Trademan t) method:

company.addTrademan(Trademan t){

users.add(t);

t.setCompany(this);

}

Call this in a transactional method.

Juan

2013/5/21 Nermin <use...@gmx.de>

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[Alfredo Quiroga]

Or use a cascade persist, merge to force creation or merge respectively

Sent from my iPhone

[Nermin]

Dear Alfredo and Juan,

obviously there is an hidden problem with my code i simply do not see.
Could you please have a short look at these 3 classes (full code) and tell me what am I doing wrong here:

https://dl.dropboxusercontent.com/u/2983671/JPA_Problem/JPA_Problem.zip

Please note: Everything works fine as log as I do not try to make any changes to the Tradesman entity (its parameters).
When is set new password or any other parameter, i get an error message of type:

Detected attempt to establish Company(no-id-yet) as the parent of Tradesman(358) but the entity identified by Tradesman(358) has already been persisted without a parent.  A parent cannot be established or changed once an object has been persisted.

I am using: JPA with DataNucleus on Google Datastore. (Standard setting that come with GWT 2.5)

Thank you in advance for your help!!

Best regards:

Nermin

2013/5/21 Nermin <use...@gmx.de>

2013/5/21 Thomas Broyer <t.br...@gmail.com>

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[Juan Pablo Gardella]

Show how you are persisting the entities.

2013/5/22 Nermin <use...@gmx.de>

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[Nermin]

Dear Juan,

For this purpose I use the GWT-s Request Factory.
However, in order to simplify the problem, I have created a server side persistence example using a simple servlet where one company and two users are created. Please have a look at the MyTestServlet.java within the Zip File.

https://dl.dropboxusercontent.com/u/2983671/JPA_Problem/JPA_Problem.zip

The funny thing is, I get now a different Eror:

javax.persistence.PersistenceException: Illegal argument
....
Caused by: java.lang.IllegalArgumentException: cross-group transaction need to be explicitly specified, see TransactionOptions.Builder.withXGfound both Element {
  type: "Tradesman"
  id: 361
}
 and Element {
  type: "Tradesman"
  id: 362
}

When I remove the @PrePersit from "User class" it works just fine!
The Error pops up as soon as i modify a parameter on "Tradesman" entity (more exactly on its parent class "User").

I really do not understand this behavior. ... I also must admit that I am not very advanced in JPA.

Thank you for very much for your help.

Best regards:

Nermin

[Juan Pablo Gardella]

In the loop, do user.setCompany(company). You need a transaction. Create it and do the commit.

2013/5/23 Nermin <use...@gmx.de>

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[Nermin]

When I try to do that, I get a following error:

java.lang.NullPointerException
	at com.google.appengine.datanucleus.StoreFieldManager.storeRelations(StoreFieldManager.java:848)
	at com.google.appengine.datanucleus.DatastorePersistenceHandler.insertObjectsInternal(DatastorePersistenceHandler.java:367)
	at com.google.appengine.datanucleus.DatastorePersistenceHandler.insertObject(DatastorePersistenceHandler.java:218)
	at org.datanucleus.state.JDOStateManager.internalMakePersistent(JDOStateManager.java:2377)
	at org.datanucleus.state.JDOStateManager.flush(JDOStateManager.java:3769)
	at org.datanucleus.state.JDOStateManager.getExternalObjectId(JDOStateManager.java:1088)
	at org.datanucleus.state.JDOStateManager.getObjectId(JDOStateManager.java:958)
	at com.emajstor.server.persistence.Company.jdoGetObjectId(Company.java)
	at org.datanucleus.api.jpa.JPAAdapter.getIdForObject(JPAAdapter.java:272)
	at com.google.appengine.datanucleus.EntityUtils.getKeyForObject(EntityUtils.java:245)
	at com.google.appengine.datanucleus.EntityUtils.getParentKey(EntityUtils.java:853)
	at com.google.appengine.datanucleus.StoreFieldManager.establishEntityGroup(StoreFieldManager.java:939)
	at com.google.appengine.datanucleus.DatastorePersistenceHandler.insertObjectsInternal(DatastorePersistenceHandler.java:244)
	at com.google.appengine.datanucleus.DatastorePersistenceHandler.insertObject(DatastorePersistenceHandler.java:218)
	at org.datanucleus.state.JDOStateManager.internalMakePersistent(JDOStateManager.java:2377)
	at org.datanucleus.state.JDOStateManager.flush(JDOStateManager.java:3769)
	at org.datanucleus.ObjectManagerImpl.flushInternalWithOrdering(ObjectManagerImpl.java:3884)
	at org.datanucleus.ObjectManagerImpl.flushInternal(ObjectManagerImpl.java:3807)
	at org.datanucleus.ObjectManagerImpl.flush(ObjectManagerImpl.java:3747)
	at org.datanucleus.ObjectManagerImpl.preCommit(ObjectManagerImpl.java:4137)
	at org.datanucleus.ObjectManagerImpl.transactionPreCommit(ObjectManagerImpl.java:428)
	at org.datanucleus.TransactionImpl.internalPreCommit(TransactionImpl.java:400)
	at org.datanucleus.TransactionImpl.commit(TransactionImpl.java:288)
	at org.datanucleus.ObjectManagerImpl.close(ObjectManagerImpl.java:1090)
	at org.datanucleus.api.jpa.JPAEntityManager.close(JPAEntityManager.java:193)
	at com.emajstor.server.persistence.Company.persist(Company.java:110)
	at com.emajstor.server.test.MyTestServlet.testPersistenceOne(MyTestServlet.java:74)
	at com.emajstor.server.test.MyTestServlet.doGet(MyTestServlet.java:39)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
	at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:123)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:61)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
	at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
	at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
	at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
	at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
	at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:94)
	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
	at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:383)
	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
	at org.mortbay.jetty.Server.handle(Server.java:326)
	at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
	at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
	at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:547)
	at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
	at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
	at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
	at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

[Nermin]

Dear Juan, Dear GWT Group

thank you very much for your help. I fixed most of my problems by following your advice. All @OneToMany relations work fine after I made sure the @ManyToOne relation is populated manually as you suggested.

Unfortunately I cannot get @OneToOne relation running wen @PrePerist is used on a child.

My sample code is here:
https://dl.dropboxusercontent.com/u/2983671/JPA_Problem/JPA_Problem.zip

Two Classes: CompanyX, TradesmanX
CompanyX stays in a OneToOne owned relation with TradesmanX
I use @PrePersist on TradesmanX in order to pre-set some fields before the Object gets persisted in the DB.

@Entity
public class CompanyX {
...
    @OneToOne(cascade=CascadeType.ALL)
    private TradesmanX adminUser;
}


@Entity
public class TradesmanX {
...
    @PrePersist
    public void myMethod(){
        System.out.println("Pre Persist");
        this.setFirstName("USER_XXXXX");
    }
...
}

//Here is how I persist them within my test servlet:

    private void testPersistenceTwo() {

        CompanyX company = new CompanyX();
        company.setName("my Comp");

        TradesmanX user = new TradesmanX();
        user.setFirstName("Test_FName");
        user.setLastName("Test_Lname");
          
        company.setAdminUser(user);
        company.persist();
    }


I am getting a similar error to the previous one:
javax.persistence.PersistenceException: Detected attempt to establish CompanyX(no-id-yet) as the parent of TradesmanX(7) but the entity identified by TradesmanX(7) has already been persisted without a parent.  A parent cannot be established or changed once an object has been persisted.

Is there a solution for this?
Would it be possible to provide some working example?

Thank you in advance:

Nermin

[Juan Pablo Gardella]

I've assumed you are trying to use unidirectional mapping. Check http://uaihebert.com/?p=1674&page=19

2013/6/5 Nermin <use...@gmx.de>

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[Nermin]

Dear Juan,

thank you for a fast reply.
Yes I would like to use unidirectional mapping, but in combination with @PrePersist method at a child entity which changes one parameter value.

Here is my code:

@Entity
public class CompanyUD {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @org.datanucleus.api.jpa.annotations.Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value = "true")
    private String id;
   
     @OneToOne(cascade=CascadeType.ALL)
     @JoinColumn(name="admin_user")
     TradesmanUD adminUser;
   
    private String name;

.. get / Set
}

@Entity
public class TradesmanUD {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @org.datanucleus.api.jpa.annotations.Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value = "true")
    private String id;
   
    private String name;

//    @PrePersist
//    public void myPrePers(){
//        setName("Some different Name");
//    }
   
   
.. get / set
}

// ====== My call:

    private void testOneToOne() {
        CompanyUD company = new CompanyUD();
        company.setName("MyTest Company");
       
        TradesmanUD user = new TradesmanUD();
        user.setName("My test Admin");
       
        company.setAdminUser(user);
       
        EntityManager em = emfInstance.createEntityManager();
        em.persist(company);
        em.close();
    }

The code above works fine without the @PrePersist method at TradesmanUD (UD stays for unidirectional)

With @PrePersist in place i get the following ERROR:

Detected attempt to establish CompanyUD(no-id-yet) as the parent of TradesmanUD(52) but the entity identified by TradesmanUD(52) has already been persisted without a parent.  A parent cannot be established or changed once an object has been persisted.

I am using JPA with DataNucleus on Google Appengine.

Thank you for your help!

Nermin

[Nermin]

I finally got it.

after investing several days for fixing this issue and after beeing very close to give up and switch over from GAE & Datanucleus to something I was more familiar with like RDBMS and Hybernate, I finally got my JPA Application up and running!! @PrePersist experience was a real pain in the ass. Unfortunately most examples which I have found on the web consider only very simple problems such as using @PrePersist on a single entity with no owned relations. However, my application is slightly more complex that :D

The reason for all this struggling and time waste was simply the fact that ONE CANNOT USE @PrePersist, nor any other callback method, on entities from owned relations.
What does this mean: if one entity called "Company" has an owned OneToOne relation with another entity called Tradesman ... YOU CANNOT USE @PrePersist at Tradesman entity and set some parameters there. This will cause you all these errors you see in my previous posts.
Instead you should use @PrePersist on Company entity (the base-entity you are trying to persist) and change Tradesman-s parameter values from there.
I presume that CascadeType.PERSIST is set to the @OneToOne relation (Company -> Tradesman).

I am quiet unhappy with the "mostly meaningless" Error Messages which I received from DataNucleus.
I would appreciate if Datanucleus Developers would pay attention to this.

My very best wishes to Juan, and other folks, who offered their help to me.

Cheers:

Nermin

[Juan Pablo Gardella]

Thanks for sharing, do you have a link where this is explained? Could you test update the field directly (without call the setter method)? Perhaps this is the problem.

Juan

2013/6/6 Nermin <use...@gmx.de>

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