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

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

2013/5/23 Nermin <user113@gmx.de>

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


Am Mittwoch, 22. Mai 2013 15:28:50 UTC+2 schrieb Juan Pablo Gardella:

Show how you are persisting the entities.

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

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


Am Dienstag, 21. Mai 2013 18:29:54 UTC+2 schrieb Alfredo Quiroga-Villamil:

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

Sent from my iPhone

On May 21, 2013, at 7:02 AM, Juan Pablo Gardella <gardella...@gmail.com> wrote:

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>

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

Am Dienstag, 21. Mai 2013 12:01:43 UTC+2 schrieb 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>

On Tuesday, May 21, 2013 11:18:42 AM UTC+2, Nermin wrote:

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?

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

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