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Date: Fri, 20 Nov 2009 21:31:33 +0100
Message-ID: <1434b04c0911201231x606d1845o431872f58f314eb4@mail.gmail.com>
Subject: Re: Migration strategy from Hibernate
From: Sebastian Wagner <seba.wagner@gmail.com>
To: users@openjpa.apache.org
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wow, that is quite extended material, thanks for the link.
I will study and come back.


sebastian

2009/11/20 Kevin Sutter <kwsutter@gmail.com>

> Hi Sebastian,
> I'm sorry to day that we don't have a cookbook on this Hibernate migration
> exercise.  I would highly suggest (beg?) that you take good notes during
> this migration so that we can all learn from the experience.
>
> I'm assuming you are moving from Hibernate "classic", meaning pre-JPA
> programming model.  Otherwise known as the Hibernate Session programming
> model.  If you are actually on moving from Hibernate JPA to OpenJPA, then
> the migration should be relatively straight forward.  But, from the content
> of your notes below, I believe you are migrating from "classic" to OpenJPA.
>
> To that end, a colleague of mine and myself have written a white paper [1]
> outlining the common Hibernate "classic" programming model paradigms and
> how
> to best map them to OpenJPA.  So, I would start with that white paper and
> see it gets you started.
>
> Also, OpenJPA supports both Annotations and XML, so if you feel more
> comfortable with the XML configuration approach, you could stick with that.
>
> I hope this helps.
> Good luck and let us know how it goes!
> Kevin
>
> [1]
>
> http://www.ibm.com/developerworks/websphere/techjournal/0708_vines/0708_vines.html
>
> On Fri, Nov 20, 2009 at 3:47 AM, Sebastian Wagner <seba.wagner@gmail.com
> >wrote:
>
> > hi,
> >
> >
> > in follow up from a discussion on the Apache General List:
> >
> >
> http://mail-archives.apache.org/mod_mbox/incubator-general/200911.mbox/%3C1434b04c0911200121g2d99f359m9c27fa41fe63ac72@mail.gmail.com%3E
> >
> > I have some quite basic questions about migrating a existing Project
> using
> > Hibernate to openJPA.
> >
> > We are using a Hibernate 3.4 + XDoclet2 to generate the HBM files.
> > We don't use a Spring Managed Transaction Manager yet for handling the
> > Session (but we should).
> > We have a lot of HQL Statements in the Code.
> > The project is: http://openmeetings.googlecode.com
> > (For anybody interested the Sources are located into
> >
> >
> http://openmeetings.googlecode.com/svn/trunk/singlewebapp/src/app/org/openmeetings/app/
> > )
> > And we are applying for Apache Incubation, so we have to get rid of
> > Hibernate.
> >
> > What is your general advice on an easy way to migrate to openJPA?
> >
> > Writing the intermediate database description per object, you use
> > annotations I guess?
> > In what kind of Java-Structure do you Map Many-To-One relations?
> > How do you handle Multi-Threaded Applications and Database Caches? In
> > hibernate a very common problem is that you have problems with Objects
> that
> > are several times in the Cache but in different Threads. In that case a
> > Session.flush does not really work as it only flushs one Thread. This can
> > be
> > solved in Hibernate by using a Spring managed Transaction Manager. What
> is
> > JPAs approach in that area?
> > And finally => HQL Statements, I guess I have to rewrite them all, but is
> > the openJPA *JPQL* very different from that? From what I have seen its
> not
> > that big Issue to refactor those statements to JPQL.
> >
> > And I have a lot more questions before I can finally decide on what is
> the
> > best and feasable way to migrate.
> > But I am eager to learn ^^ so maybe somebody is eager to give us some
> tipps
> >
> > I will try to study the docs,
> > but i have not seen any kick-start example yet that covers the most of
> > basic
> > topics. Is there any sample that can be re-used?
> >
> >
> > thanks a lot
> > Sebastian Wagner
> >
> > --
> > Sebastian Wagner
> > http://www.webbase-design.de
> > http://openmeetings.googlecode.com
> > http://www.laszlo-forum.de
> > seba.wagner@gmail.com
> >
>


-- 
Sebastian Wagner
http://www.webbase-design.de
http://openmeetings.googlecode.com
http://www.laszlo-forum.de
seba.wagner@gmail.com

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