Consider the following scenario. Your customer has a Web-based reporting system that uses client-side Internet Explorer (IE) data islands. The current version pulls all the records to the client at once and uses Extensible Style Language Transformations (XSLT) on the client side to transform the data to a columnar format. This version also has client-side data sorting (by clicking on the field column). Your customer wants to change this system to one that pages the data to the client, 25 records at a time, to speed up the report's initial presentation—downloading and performing transformations on a few thousand records is too slow. But the customer, of course, still wants to sort the data by the field columns and to be able to view all the records.
When the report returns the records from the query, you could simply display the first 25 records. Then if a user pages ahead, you could display the next 25 records. But running the query every time seems like a waste of resources. You could use ADO to page the records down, but you need a stateless design (this Web site is, after all, WELL designed). You could use some fancy, elaborate, "smart" stored procedure that creates a temporary table for every user who runs the report and then perform selects out of the temporary table for the paged records. But that's a lot of hits to the database and a lot of maintenance to get rid of the huge number of temporary tables. I'm going to share with you an XML solution that I used to tackle this very scenario—using Windows 2000, SQL Server 2000, IE 5.0+, and Microsoft XML Parser (MSXML) 3.0.
My solution uses a data island—not a client-side, IE data island, but a server-side file data island. Below is the pseudocode for the solution:
If this is the first run of the query then Run the query Save the resulting XML to a file on the server Set the start record number to 0 and the last record number to 25 Else if paging forward Add 25 to the start record number and the last record number Else if paging back Subtract 25 from the start record number and the last record number End if If resorting then Transform the XML data island file with an XSLT file that resorts the records Overwrite the XML file on the server with the resulting XML End if If displaying all records then Use the entire XML data island file Else Use an XSLT file to select the records between start record number and last record number from the XML data island file End if Send the XML to the client
Voila! Trust me, this approach is much simpler than it sounds. You simply need five hidden input tags on the report page that you post over:
- a hidden input that holds the current first-record number on the page
- a hidden input that holds the desired action (e.g., show first page, page up, page down)
- a hidden input that holds the field to sort by
- a hidden input that holds the sort direction
- a hidden input that holds the sort field's date type
You need to either pass parameters to your Extensible Style Language (XSL) files or use the Document Object Model (DOM) to change the paging range of the pagination XSL file and the sorting properties of the re-sorting XSL file.
The pagination and the re-sorting code appear below.