[jira] Commented: (DISPL-14) Smart Paging

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[jira] Commented: (DISPL-14) Smart Paging

JIRA jira@codehaus.org
    [ http://jira.codehaus.org/browse/DISPL-14?page=comments#action_42573 ]

Matthew Payne commented on DISPL-14:

You guys have like 5+ different issues that are vitually the same(paging big results) someone link them in jira.

> Smart Paging
> ------------
>          Key: DISPL-14
>          URL: http://jira.codehaus.org/browse/DISPL-14
>      Project: DisplayTag
>         Type: Improvement
>   Components: Paging/Sorting
>     Versions: 1.0 RC2
>     Reporter: fabrizio giustina
>     Assignee: fabrizio giustina
>  Attachments: OptimizedPaginationIteration.1.0-RC2.zip, OptimizedPaginationIteration.zip, displaytag-1.0-rc1-pdf_paging_exclude_columnhref.diff, dt_pdf_paging.diff, dt_pdf_paging_java.zip
> ====
> imported from sf tracker
> id 1026408
> submitted by Ivan Markov - ivan_markov
> http://sourceforge.net/tracker/index.php?func=detail&group_id=73068&atid=536613&aid=1026408 
> ====
> Smart Paging
> ------------
> Smart paging refers to the ability of DT to deal with large lists of data. The problem with the current DT approach is that:
> a) The whole (potentially large) list of data has to be created for the DT tag, occupying lots of memory.
> b) If the list contains 1000s of records, populated with data from a SQL Server (99% of the cases, I would say), you have huge network traffic between the webapp and the server. Our code is especially useful for servers like Oracle & MySQL which have built-in means to return only a subset of DB cursor's content.
> There's one solution + one enhancement on the forums already (issue #1013526), so why a third one?
> We didn't like in the earlier proposal that it deals with intercepting DT's request and parsing DT's request parameters, which seems a bit hacky. Also, we avoid the complications of parsing parameters when there is > 1 table tag on the page. Not to mention that the older proposal does not deal with full list sorting, or does it?
> Instead, we introduced a new interface, DataProvider. It has two methods:
> - List getData(int unsortedOffset, int unsortedLength, int recordOffset, int pageSize, String sortedColumnName, boolean sortOrderAscending);
> - int getDataCount();
> The first two parameters unsortedOffset & unsortedLength are only needed for supporting DT's setOffset()/setLength() features.
> In our patch, DataProvider is used as a "callback" into user's code. The user is supposed to implement the two methods of this interface.
> The code in TableTag and its supporting classes is changed in a way that, for each response where DT is rendered,
> a) One call is issued to DataProvider.getDataCount(), which retrieves the total number of rows in the data set (needed for DT to calculate the number of pages).
> b) One call is issued to DataProvider.getData(), with the current page, page size & sorting info.
> A sample implementation of user-supplied JDBC DataProvider follows, in pseudocode. Some JDBC exception handling stuff omitted.
> <%
> request.setAttribute("list", new DataProvider() {
>     List getData(int unsortedOffset, int unsortedLength, int recordOffset, int pageSize, String sortedColumnName, boolean sortOrderAscending) {
>     Connection con = <app-specific way to get connection>;
>     PreparedStatement ps = con.prepareStatement("SELECT * FROM MyTable ORDER BY ? LIMIT ?, ?"):
>     ps.setString(1, sortedColumnName);
>     ps.setInt(2, recordOffset);
>     ps.setInt(3, pageSize);
> //etc..    
>     ResultSet rs = con.execute();
>     return <app-specific way of getting List from ResultSet; Maybe use RowSet instead of List?>;
>     }
>     int getDataCount() {
>     Connection con = <app-specific way to get connection>;
>     PreparedStatement ps = con.prepareStatement("SELECT count(*) FROM MyTable"):
>     ResultSet rs = con.execute();
>     rs.next();
>     return rs.getInt(1);
>     }
> });
> %>
> (DataProvider implementation code can be moved to Struts Controller/Action, depending on the MVC framework used, in order not to polute the JSP code with Java scriptlets.)
> Smart Paging Compatibility
> --------------------------
> We tried to change DT's code so that all older code to continue to work.
> If user has provided an old-style List containing all the data, DT will automatically wrap it with a ListDataProvider.
> Current DT functionality (full-list sorting, decorations, multiple tables per page, etc.) is supported, except for these two cases:
> a) Full list(not page) sorting by a decorated column - sorting is done without regarding the decorator.
> b) Full list sorting by a column with no "property" attribute (static or implicit object call via servlet) - no sorting is performed at all.

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