On 11/24/06, Korbinian Bachl <[EMAIL PROTECTED]> wrote:
Remember Also remember
that its always a question how you access data (plain JDBC, JDO, JPA etc.)
to have a good solution.
it doesnt matter how you access data.
the only assumption made is that it is cheaper to retrieve a (total
count+window) rather then (the entire dataset), which holds true almost
always. some exceptions being an in-memory database.
-igor
Best Regards
> -----Ursprüngliche Nachricht-----
> Von: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] Im Auftrag
> von Frank Silbermann
> Gesendet: Freitag, 24. November 2006 15:25
> An: [email protected]
> Betreff: Re: [Wicket-user] SortableDataProvider, size() &
> iterator(int first,int count), Correct execution order?
>
> About DataTable and SortableDataProvider, I believe the
> designer's assumptions are that in typical use:
>
> (1) the DataProvider will not cache any data,
>
> (2) each call to iterate() will do a select from the database,
>
> (3) each call to size() will do a select from the database, and
>
> (4) the number of elements in the database will not change
> between calls (or if the data does change, we don't care that
> the screen might show inconsistent results as the user pages
> back and forth).
>
>
> What if we want the pages to show a consistent view, even
> though the data might change as the user is paging through
> it? If the data volume is not too huge, I suppose one could
> page through a snapshot of the data. To me, that suggests
> putting all the data in the webpage and using JavaScript to
> page through it without resubmitting. However,
> Wicket-Extensions provides no widget with this sort of
> client-side functionality. Even if we had such a widget, its
> use would be impractical if the dataset were too huge for a
> single page download.
>
> What one can do with the current DataTable -- at least if the
> number of concurrent users is small and the size of the
> result set is reasonable
> -- is to have the SortableDataProvide retrieve all the data
> at once and cache it in session storage between pages. Since
> we don't know whether
> size() or iterate() will be called first, each will have to
> check whether the data has already been obtained, and if not
> then to obtain the data for both methods to use.
>
>
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf
> Of Manuel Barzi
> Sent: Thursday, November 23, 2006 6:25 AM
> To: [email protected]
> Subject: [Wicket-user] SortableDataProvider, size() &
> iterator(int first,int count), Correct execution order?
>
> Hi, there,
>
> I have the following composition:
>
> WebPage >...
>
> ... DataView > CustomProvider extends SortableDataProvider
>
> ... PagingNavigator > DataView
>
> The ERROR? I found is this:
>
> When clicking on any of the navigation buttons
> (PagingNavigator), my CustomProvider implementation is
> managed by Wicket FW calling its implemented (abstract in
> SortableDataProvider) in the following order:
>
> 1 size()
> 2 iterator(int first, int count)
>
> That causes wrong results, because it calls first the size()
> to check the results obtained when I havent called the
> iterator(...) yet, and inside my implementation of
> iterator(int first, int count) I obviously do the call to the
> API that accesses to my persistent layer obtaining the
> results according to the specified (first, count) pair...
>
> So, what happens in practice... that when navigating the
> size() method retrieves the before obtained iterator.size(),
> and not the new one that will be obtained immediatly after
> it, when calling to iterator(...).
>
> So, if the order was this:
>
> 1 iterator(...)
> 2 size()
>
> The problem would be solved...
>
> Please, would you mind explaining my how to resolve this issue?
>
> Thank you!
>
> M
>
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