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From Arnaud Garcia <arn...@imagemed-87.com>
Subject Re: Wicket Cayenne
Date Sat, 24 Apr 2010 18:42:44 GMT
I did some tests, maybe it can interest you...,
(these are some reflexions on my pretty bad  understanding of Cayenne, so I
apolosize if it is wrong, it is my first cayenne/wicket project)

If technically it seems ok to put the DataContext in the user session and
retrieve it, as a normal java object,   then you can remove the Cayenne
Filter from your web.xml, because you don't need it anymore, since you are
in charge of the DataContext creation.

I try it and :

WicketMessage: Can't instantiate page using constructor public
org.....HomePage()

Root cause:

java.lang.IllegalStateException: Current thread has no bound ObjectContext.
If you look at the Cayenne Filter, it creates a DataContext and the bind it
to the current Thread.
So, using the same idea, you to rewrite your function like this:
public DataContext getSessionDataContext(){
       synchronized(this){
           if(this.dataContext==null){

BaseContext.bindThreadObjectContext(DataContext.createDataContext())
               this.dataContext =   dataContext = (DataContext)
DataContext.getThreadObjectContext();

           }
       }
       return this.dataContext;
   }

So  I think, the Cayenne DataContext has to be related to the current thread
and not to the user session.

Do you have an idea why the DataContext is bind to the current thread and
not to the user session ?


2/ About Wicket, what do you mean by " Wicket users are abstracted from
HTTPSession" ?


Arnaud



2010/4/24 Nishant Neeraj <nishant.has.a.question@gmail.com>

> weirdly, while implementing I had the same doubt. Seeing into the doc
> here[1] or better here[2], I realized that the idea suggested for web-apps
> does not fit for Wicket because Wicket users are abstracted from
> HTTPSession.
>
> Looking into  the code on how the servlet does this thing, in the method
> org.apache.cayenne.conf.ServletUtil.getSessionContext(..) -- this is what
> being done. see code snippet below. So, I did not evaluate much on gain in
> using getThreadObjectContext() vs CreateDataContext() -- since the
> Cayenne's
> native implementation does that way therefore I followed.
>
> On thinking about this now, I think createDataContext() must not be a loss
> in performance, because what we are doing, basically, is creating context
> at
> session start and holding the instance of DataContext all the time until
> session expires -- so it should be, I hope, at least same as using
> getThreadObjectContext().
>
> But I would like to know if there is a flaw in my thinking.
>
>
> [CODE]
>   /**
>     * Returns default Cayenne DataContext associated with the HttpSession,
> creating it on
>     * the fly and storing in the session if needed.
>     */
>    public static DataContext getSessionContext(HttpSession session) {
>        synchronized (session) {
>            DataContext ctxt = (DataContext)
> session.getAttribute(DATA_CONTEXT_KEY);
>
>            if (ctxt == null) {
>                ctxt = DataContext.createDataContext();
>                session.setAttribute(ServletUtil.DATA_CONTEXT_KEY, ctxt);
>            }
>
>            return ctxt;
>        }
>    }
>
> [/CODE]
>
>
> [1] http://cayenne.apache.org/doc30/obtaining-datacontext.html something's
> wrong, all the code snippets are gone!
> [2]
>
> http://74.125.153.132/search?q=cache:HFEZ2Rs496UJ:cayenne.apache.org/doc20/obtaining-datacontext.html+http://cayenne.apache.org/doc30/obtaining-datacontext.html&cd=1&hl=en&ct=clnk&gl=in&client=firefox-a
>
>
> - Nishant
>
> On Sat, Apr 24, 2010 at 6:06 PM, Arnaud Garcia <arnaud@imagemed-87.com
> >wrote:
>
> > ... OK, putting the dataContext in the session object is certainly a good
> > idea, but for the creation of the DataContext do you think we have to use
> > the createDataContext() or using the DataContext.getThreadObjectContext()
> > since it is supposed to be attached to the current thread by the cayenne
> > filter ...
> >
> > Arnaud
> >
> > 2010/4/24 Nishant Neeraj <nishant.has.a.question@gmail.com>
> >
> > > Hi Arnaud,
> > >
> > > I have used session to store my dataContext
> > >
> > > something like this
> > >
> > > public DataContext getSessionDataContext(){
> > >        synchronized(this){
> > >            if(this.dataContext==null){
> > >                this.dataContext = DataContext.createDataContext();
> > >            }
> > >        }
> > >        return this.dataContext;
> > >    }
> > >
> > >
> > > anywhere I need this, I perform this
> > >
> > > DataContext dctx =
> ((MyAppSession)getSession()).getSessionDataContext();
> > >
> > > I think it may not solve the serialization issue, if session objects
> are
> > > serialized. But you avoid creating DataContext at every page.
> > >
> > > Not sure if this helps you.
> > >
> > > You may want to see how DataBinder[1] has implemented it.
> > >
> > > [1] http://databinder.net/wicket/show/overview/
> > >
> > > - Nishant
> > >
> > > On Sat, Apr 24, 2010 at 1:55 PM, Arnaud Garcia <arnaud@imagemed-87.com
> > > >wrote:
> > >
> > > > Hello,
> > > >
> > > > I put my question in both forum, (wicket and this one)
> > > >
> > > > Does anyone knows how to set up Cayenne for wicket ?
> > > >
> > > > In my WicketPage I have :
> > > >  private DataContext ctxt = (DataContext)
> > > > DataContext.getThreadObjectContext();
> > > >
> > > > but, I don't think it is the good way, since I suppose wicket will
> > > > serialized the full DataContext... (maybe I can put the
> > > > getThreadObjectContext() in a method or constructor to avoid the
> > > > serialization...)
> > > > -> Well, I don't know how what is the good way  ;-)
> > > >
> > > >
> > > >
> > > > thanks,
> > > >
> > > > Arnaud
> > > >
> > >
> >
>

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