Hi Markus,
Thanks for documenting this all.
Do you want to add this yourself to the FAQ on the Wiki?
http://wiki.glassfish.java.net/Wiki.jsp?page=GlassFishUserFAQ
thanks,
-Alexis
On Jan 4, 2008, at 9:44, Markus KARG wrote:
> Marina,
>
> thank you for your kind answer.
>> The JPA spec in the section 9.1.9 GeneratedValue Annotation says
>> about various strategies: "This specification does not define the
>> exact behavior of these strategies.". It might be a known bug in
>> TopLink, but we always advised to call em.flush() if somebody
>> needed to get a hold of the generated PK.
> You are absolutely right, I was just blind that day. ;-)
>
> In particular, I found the following in JPA 1.0 specification
> chapter "3.2.1 Persisting an Entity Instance":
>
> "A new entity instance becomes both managed and persistent by
> invoking the persist method on it or by cascading the persist
> operation. The semantics of the persist operation, applied to an
> entity X are as follows: • If X is a new entity, it becomes managed.
> The entity X will be entered into the database at or before
> transaction commit or as a result of the flush operation."
>
> Okay, that says it all: A user MUST invoke flush() or commit() to
> make the O/R mapper talk to the database server, so it is NOT a bug,
> neither of TopLink in general, nor of the particular part of TopLink
> that I wrote. That completely and unambigously answers my question.
> Once more it was helpful to ask before filing a bug report. :-)
>
> For all people scanning the mailing list for a solution to the same
> problem, here is the corrected code that works pretty well:
>
> em.getTransaction().begin();
> Article a1 = new Article();
> em.persist(a1);
> em.flush(); // <--- FLUSH (OR COMMIT) IS NEEDED HERE
> System.out.println(a1.getId()); // Prints: 60 // Prints: 0 WITHOUT
> flush() or commit()
> Article a2 = em.find(Article.class, 60);
> System.out.println(a2.getId()); // Prints: 60
> em.getTransaction().commit();
>
> Maybe someone likes to add this snippet tho the user's FAQ. :-)
>
> Thanks for pointing me in the right direction!
>
> Have Fun
> Markus
>>
>> Regards,
>> -marina
>>
>> Markus KARG wrote:
>>> Hi all,
>>>
>>> as you know, I am the author of the Sybase support in TopLink
>>> Essentials. :-)
>>>
>>> I just tried a short code snipped and noticed a strange behaviour.
>>> Since I do not know whether that is wanted by JPA spec, or a bug
>>> of TopLink, or a bug of my own code, I want to discuss with you
>>> prior to filing a bug report.
>>>
>>> See the following code snippet:
>>>
>>> em.getTransaction().begin();
>>> Article a1 = new Article();
>>> em.persist(a1);
>>> System.out.println(a1.getId()); // Prints: 0
>>> Article a2 = em.find(Article.class, 60);
>>> System.out.println(a2.getId()); // Prints: 60
>>> em.getTransaction().commit();
>>>
>>> "Article" is an entity that is using IDENTITY strategy for
>>> generating its primary key:
>>>
>>> @Id
>>> @GeneratedValue(strategy = GenerationType.IDENTITY)
>>> private int id;
>>>
>>> The database wrapper used, obviously, is the one I wrote. ;-)
>>>
>>> As you can see, when asking for the generated ID directly after
>>> em.persist(a1), it returns the wrong value of 0. In fact, it
>>> certainly shall tell the actually generated value of 60, since it
>>> is impossible to know that value -- and such it is impossible to
>>> ask for that PK explicitely as I have done it in the em.find()
>>> line. But knowing the PK might be critical to some use cases. In
>>> fact, my Sybase wrapper included in TopLink so far has code that
>>> reads back the created value -- but it seems that value gets lost
>>> "somewhere". I know that somebody changed my code recently to
>>> support IDENTITY and SEQUENCE strategy at the same time. Maybe he
>>> broke it?
>>>
>>> So my question is: IS THAT A BUG?
>>>
>>> And if it is: Is that a bug of my Sybase wrapper, or a bug of
>>> TopLink?
>>>
>>> Thanks
>>> Markus
>>>
>>
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>
>
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>
>