Re: Question With Detachable Models
we're just quibbling over what stored in the session means. if we mean (as it seems obvious i did) is it reachable through the wicket session on the web node and does it take up memory on that node then yes it is in some sense it is stored in the (wicket) session (it's there in the debugger and taking up session-associated resources). if on the other hand we mean (as it's obvious you did) is it is part of the (container) replicated session, as reconstructed from disk or on other web nodes via serialization then it's obviously not stored in the (container) session because nothing transient can ever be serialized by definition. we were just talking past each other. Kent Tong wrote: 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. Are you sure about that? If the default item reuse strategy is used, new models and new items will be created just before the page is rendered. In addition, as the object instance is marked as transient, it shouldn't be stored in the session. -- View this message in context: http://www.nabble.com/Question-With-Detachable-Models-tf4446686.html#a12697727 Sent from the Wicket - User mailing list archive at Nabble.com. - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Question With Detachable Models
hi, Are my objects still being stored in the session when I use this kind of query. transient fields are never stored in a session at all. but since you have neither an id nor a logic to load your object to be restored, you certainly will get a NPE when the object is about to be restored. regards, --- jan. - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Question With Detachable Models
transient fields are never stored in a session at all. sorry, i meant they are never serialized at all. - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Question With Detachable Models
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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Re: Question With Detachable Models
Thanks for replying
Yup thanks
I was debugging it and I was able to see it in the session object. meaning
that it is still stored in my object.
I changed the implementation to loading the object.
Now I changed it to loading it from a facade bean.
Thanks
Jonathan Locke wrote:
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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