It doesn't hold onto the persistent object. Here's an example usage:
IModel<Person> personModel = ...; // Some LDM here!
ProxyModelManager mgr = new ProxyModelManager();
add(new TextField<String>("firstName", mgr.proxy(new
PropertyModel(personModel, "firstName"))));
Then, later on in the onSubmit() method, you'd call mgr.commit().
It's not going to hold onto the object that's loaded from the LDM. It
would hold onto the property values of the object that's loaded from
the LDM, but that's okay.
On Mon, Apr 5, 2010 at 9:23 PM, Russell Morrisey
<russell.morri...@missionse.com> wrote:
> This approach stores a hard reference to the object. It seems prone to
> causing LazyInitializationExceptions when used with Hibernate. You are
> storing a reference to a persistent object (in this case, the regular Model
> object of the ProxyModel), so if you close your session at the end of the
> request, I would expect you to get this exception on the next request when
> you call a method on a lazy proxy object (ex:
> ((MyObject)model.getObject()).getLazyProperty().getName()).
>
> Do you have some other code to work around it? (like loading a fresh object
> from the session at the beginning of the request) It may be you don't hit
> this problem in your use case.
>
> RUSSELL E. MORRISEY
> Programmer Analyst Professional
> Mission Solutions Engineering, LLC
>
> | russell.morri...@missionse.com | www.missionse.com
> 304 West Route 38, Moorestown, NJ 08057
>
>
> -----Original Message-----
> From: James Carman [mailto:jcar...@carmanconsulting.com]
> Sent: Monday, April 05, 2010 9:05 PM
> To: users@wicket.apache.org
> Subject: Re: LoadableDetachable Models
>
> You can use what we call a "shadow model" or a "proxy model."
>
> https://wicketopia.svn.sourceforge.net/svnroot/wicketopia/trunk/wicketopia/src/main/java/org/wicketopia/model/proxy/ProxyModelManager.java
>
> This approach will work for you. Basically, you use the
> ProxyModelManager to "wrap" all of your real models (you have to
> explicitly create models to use this and can't use
> CompoundPropertyModel). Then, when you're done with what you're
> doing, you "commit" your changes into the real models.
>
> On Mon, Apr 5, 2010 at 6:11 PM, Russell Morrisey
> <russell.morri...@missionse.com> wrote:
>> Jeffrey,
>>
>> The problem is that if you use an LDM, the list is loaded from persistent
>> storage, and any non-persisted changes from the previous request are lost.
>> If you don't use an LDM, though, you will have stale objects hanging around
>> from the previous Hibernate session (as you mentioned).
>>
>> Think in the mindset that persistent Hibernate objects are only "valid"
>> within the context of a request. Only transient objects are safe to hold
>> references to. You can implement a custom model which keeps track of
>> transient items between requests. It can extend LDM.
>>
>> For example:
>> -Custom LDM loads the list from persistent storage
>> -User clicks a button to add an object to the list
>> -myCustomModel.addObject(newObject) is called by your ajax behavior
>> (triggered by the click)
>> -The list is modified, and your model internally stores a list of transient
>> objects which were added or removed
>> -On the next request, your implementation of load() can get the persistent
>> list from the database, and modify it according to the un-persisted changes
>> the model knows about (make a copy of the list and add or remove the
>> transient items).
>>
>> If you don't like putting a method like addObject(...) on your model, you
>> could put some logic in your setObject(...) method which sorts out the
>> changes made to the list. You should not hold a reference to a persistent
>> object after detach(). A tool like JProbe or jvisualvm (in JDK6) is great
>> for identifying problem cases.
>>
>> If you have a component who depends on the data from another component with
>> unsaved changes, you can submit data for the "prerequisite" in the same
>> request, so that the information is current.
>>
>> HTH,
>>
>> RUSSELL E. MORRISEY
>> Programmer Analyst Professional
>> Mission Solutions Engineering, LLC
>>
>> | russell.morri...@missionse.com | www.missionse.com
>> 304 West Route 38, Moorestown, NJ 08057
>>
>> -----Original Message-----
>> From: Jeffrey Schneller [mailto:jeffrey.schnel...@envisa.com]
>> Sent: Monday, April 05, 2010 3:26 PM
>> To: users@wicket.apache.org
>> Subject: LoadableDetachable Models
>>
>> I am having issues with LDM, Hibernate lazy loaded lists, and ajax.
>>
>>
>>
>> I create a CompoundPropertyModel of a LDM and set that as the default
>> model for the page.
>>
>> I then pass the model to the form and to a custom component in the form.
>> The custom component is a list editor. Basically a ListView with lots
>> of ajax link for editing the values.
>>
>>
>>
>> The issue I am having is I can get everything to work however because of
>> the LDM, the model is being over-written on each Ajax request and also
>> on form submission so I cannot modify any values since they are not
>> available in the onsubmit because the LDM reloads.
>>
>>
>>
>> If I do not use the LDM then I get Hibernate errors because of the lazy
>> loading.
>>
>>
>>
>> If I remove the lazy loading and use eager loading and don't use the LDM
>> then everything works fine. The issue is because of the eager loading
>> then other parts of the application load lots of data that is not
>> needed.
>>
>>
>>
>> Any ideas? Can I not use the LDM for what I want?
>>
>>
>>
>> Thanks.
>>
>>
>>
>>
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