Hmm, maybe I'm missing something, but if you want to have EVALUATED once per
request, I think the following should be sufficient. (unless I'm missing
somtething)
new AbstractReadOnlyModel<T>() {
private transient T cachedValue;
@Override
public T getObject() {
if (cachedValue == null) {
cachedValue = ...; //evaluate here, only once per
request
}
return cachedValue;
}
};
since the cached value is transient, it will be null when it is
deserialized. But during the requestCyclue, the evaluation will only happen
once. (at least, if I'm not missing something...)
On Sun, Oct 25, 2009 at 7:02 AM, Martin Makundi <
[email protected]> wrote:
> > What I found was that I was instantiating my LDM's as private variables
> in
> > my custom components but that they were not being detached. In this case
> > you need to programatically register your non default models to
> participate
> > in the detachment process. See the Wiki here for an example:
> >
> http://cwiki.apache.org/confluence/display/WICKET/Working+with+Wicket+models#WorkingwithWicketmodels-ManagingthelifecycleofnondefaultdetachableIModel%27s
>
> Which part there in particular? I read it and it didn't yet ring my bell...
>
> is there really "another way" to register for onDetach events apart
> from the model being directly involved in render cycle as a
> formcomponent's or another component's defaultmodel?
>
> > For your option 3 I would say you should create a custom IModel
> > implementation that is aware of your caching strategy so that your
> > Component's don't need to care about how the data is loaded.
>
> Well.. that's the dream ;) Furthermore, I would like it to be more or
> less automatic. Maybe models like:
>
> 1. SettingThisModelWillResetCacheModel extends IModel
> 2. SettingThisModelWillNOTResetCacheModel extends IModel
>
> Furthremore, they would probably be created using a factory method in
> a cache manager:
>
> CacheManager cacheManager = new CacheManager(detachableToo);
>
> cacheManager.newIndependentCachedModel(IModel ...)
> cacheManager.newCachedModelWhoseChangeFiresExpire(IModel ...)
>
> AND maybe I could chain cacheManagers to say "cache manger A will
> expire if any of its dependent managers B-C-D expire."
>
> Also it should be easy to add
> cacheManager.addCacheExpirationListener(Runnable ..) or something.
>
> ...
>
> Anybody else need something like this? We could write a draft and see
> if it works and continue improving the design.
>
> **
> Martin
>
>
> >
> > Your implementation could hold a Map of all related models and update
> > according to your rules or better yet build a service that does the
> caching
> > and dirty detection and then just have the LDM source the cell value from
> > the service. Something like:
> >
> > new LoabableDetachableModel () {
> >
> > protected CellValue load () {
> >
> > return cellService.getValue (row, col);
> > }
> > }
> >
> > Regards,
> >
> > Mike
> >
> >>> evaluated only one time per render can be done with
> >>> LoadableDetachedModel ..
> >>>
> >>
> >> I do not mean LOADED once per render. I mean EVALUATED once per
> >> render. In my understanding LoadableDetachableModel does not guarantee
> >> "reset" in any particular stage.
> >>
> >>
> >>>
> >>> can you explain it a littly bit (a link to your original message?)
> >>>
> >>
> >> I mean for rexample I have many models like this:
> >>
> >> new AbstractReadOnlyModel<String>() {
> >> public String getObject() {
> >> // evaluate message with some logic
> >> return message;
> >> }
> >> }
> >>
> >> Furthermore, I have several components that, say, depend on this
> >> value. This getObject() will be called many times durung render and
> >> the logic will be evaluated many times.
> >>
> >> If I make it detachable it will yes be detached but I am not sure that
> >> the detaching is guaranteed at some specific point in request cycle?
> >>
> >> To make my "use case" more clear I will give an example: say I have a
> >> wicket page with a panel that contains a table with columns rows and y
> >> rows. Furthermore, let's assume it is a spreadsheet emulator: you can
> >> write formulas into the cells that depend on the other cells which
> >> means that the value of each cell is recursively evaluated dependent
> >> on the other cell's values.
> >>
> >> Requirements:
> >> 1. During render time each cell's model value should be cached once it
> >> has been evaluated (we do not want to recurse many times to fetch the
> >> same value).
> >> 2. If the value of any cell changes, all the dependent cells should be
> >> (for example) ajax refreshed and re-evaluated. For simplicity, we
> >> could re-set the cache of all models when change occurs. And
> >> redraw-all.
> >> 3. We want to reset cache ONLY if change occurs.
> >>
> >> In my understanding requirement 3 cannot be directly reached with
> >> detachable models.
> >>
> >> **
> >> Martin
> >>
> >>
> >
> >
>
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