I should also add this: although you can do what you will in Wicket, it is
generally better to use models consistently and reload your objects from the
DB (this isn't so bad in practice as a lot of the time reloads will just hit
ehcache or whatever you're using to cache query results and hook the object
back up again in no time). It also shrinks the serialization overhead and
replication bandwidth required to move your objects around in the cluster
(and with SoftReferenced instance objects it could also decrease your
non-reclaimable memory load if that matters). But it is also generally
helpful to work with reloadable models because they automatically avert the
more common stale data issues you'll run into. In a multi-user system, this
is helpful. If you've got a Label whose model is a PropertyModel on a
reloadable PersonModel and someone else changes the PersonModel, the
expression being retrieved from the model will auto-update. If the label is
directly holding the POJO and it's not reloadable, the label will continue
to display the stale data forever.
Jonathan Locke wrote:
>
>
> Your QueryDetachableModel will break under clustering. The transient
> "instance" Object will become null when the container deserializes it and
> your load method will be unable to reload the object.
>
> If you're using these QueryDetachableModels, yes, the object instance is
> being stored in your session. But no, it will not be replicated
> correctly.
>
> If you really want to make the memory impact disappear as well as the
> clustering bandwidth, you would need to use a transient SoftReference and
> take the hit of implementing a load method which reads your object from
> some kind of object storage (or cache).
>
> There is no free lunch. You are ultimately stuck with a tradeoff: either
> use the memory and/or bandwidth OR be prepared to pay the price of loading
> the object from storage.
>
>
> carloc wrote:
>>
>> Hi, I would like to ask this.
>>
>> Are my objects still being stored in the session when I use this kind of
>> query.
>> I don't requery the objects using a detachable model.
>>
>> package com.ccti.web.query;
>>
>> import org.apache.wicket.model.LoadableDetachableModel;
>>
>> public class QueryDetachableModel extends LoadableDetachableModel {
>> private transient Object instance;
>>
>> public QueryDetachableModel(Object instance) {
>> this.instance = instance;
>> }
>> @Override
>> protected Object load() {
>> // TODO Auto-generated method stub
>> return instance;
>> }
>>
>> }
>>
>> Here's how my DataProvider looks like.
>>
>>
>> public class QueryDataProvider extends SortableDataProvider {
>>
>> /**
>> *
>> */
>> private transient QueryCommand queryCommand;
>>
>> public QueryDataProvider(QueryCommand queryCommand) {
>> this.queryCommand = queryCommand;
>> }
>>
>> /* (non-Javadoc)
>> * @see
>> org.apache.wicket.markup.repeater.data.IDataProvider#iterator(int, int)
>> */
>> public Iterator iterator(int first, int count) {
>> // TODO Auto-generated method stub
>>
>> setQueryLimits(first, count);
>> return queryCommand.execute();
>> }
>>
>> /**
>> * @param first
>> * @param count
>> */
>> private void setQueryLimits(int first, int count) {
>> // can't be set anywhere else but here.
>> queryCommand.setPageIndex(first);
>> queryCommand.setPageSize(count);
>> }
>>
>> public IModel model(Object object) {
>> // TODO Auto-generated method stub
>> return new QueryDetachableModel(object);
>> }
>>
>> public int size() {
>> // TODO Auto-generated method stub
>> return queryCommand.queryCount();
>> }
>>
>
>
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