[jira] Commented: (WICKET-1784) Enhance IDataProvider to support applications using the Transfer Object J2EE pattern

["Igor Vaynberg (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/WICKET-1784?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12621269#action_12621269 ] 

Igor Vaynberg commented on WICKET-1784:
---------------------------------------

so what happens if

you have a dataview that is set to show 5 items per page
during the last request you had 10 items and you are curently on page 2 (5-9)

the navigator is showing that you have 3 pages

someone deletes one item

you hit page 3  (items 10-14) on the navigator

the dataview requests iterator(10,14)

your service layer returns datawindow {count:9, iterator:empty}

the dataview renders, but how?

it cannot render page 3 in the navigator because according to size there is no such page, it also cannot render any other page as selected because it does not have data for that page

so it has to requery?

> Enhance IDataProvider to support applications using the Transfer Object J2EE pattern
> ------------------------------------------------------------------------------------
>
>                 Key: WICKET-1784
>                 URL: https://issues.apache.org/jira/browse/WICKET-1784
>             Project: Wicket
>          Issue Type: Improvement
>          Components: wicket
>    Affects Versions: 1.3.3, 1.4-M3
>         Environment: Wicket 1.3.3 and 1.4-M3
>            Reporter: R. Goodwin
>            Assignee: Igor Vaynberg
>
> In some environments searches are performed in 'single call' fashion, using a transfer object.
> E.g. two queries performed by the data services tier before returning combined results to the UI tier:
> i. Query for paged search results
> ii. Query for a 'count' value representing total possible results
> The contract between DataView and IDataProvider does not support a 'single call' environment as the give/take relationship between these classes is biased towards DataView.
> DataView expects IDataProvider to provide it's size before providing IDataProvider with its offset and count.
> * DataView may have good reasons for needing size before it can provide offset/count.
> * But IDataProvider has equally good reasons for needing offset/count before it can provide size.
> The circular dependency:
> 1. DataView calls IDataProvider.size()
> 2. IDataProvider cannot return size as it cannot start a query until it receives offset/count from DataView
> 3. These it does not receive until DataView calls IDataProvider.iterator() later on
> Others who experienced this problem (with CODE examples):
> * http://www.nabble.com/IDataProvider-and-Hibernate-Search-td15546101.html
> * http://www.mail-archive.com/users@wicket.apache.org/msg14266.html
> ---
> The suggested solution of caching the combined search results and count value does not work if the search cannot begin until offset and count are available. And writing a custom DataView is not feasible either time wise as I understand that it cannot be done without needing to write a number of other classes too.

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