Paging random data

pjskeldon · April 24th, 2013, 09:32 AM

Iâm a newcomer to ASP.NET (3 months) so am unsure how to solve this problemâ¦

I run a village website which has about 60 advertisers. The details of the advertisers are held in the SQL Server database that holds other information about the site.
One of the pages shows all 60+ adverts in a gallery, using an ASP.NET ListView control.
To avoid any advertiser being âtop of the listâ, the sequence of adverts is deliberately randomised on every visit using âORDER BY NEWID()â in the SQL retrieval statement.

Iâd like to reduce this long page to show only 6 at a time, with buttons to navigate back and forth, and have done this with a DataPager control and AJAX to minimise flicker (pages 544-549 of Imar's Beginning ASP.Net 4.5 book)

However, when I page back and forth the pages show different content each time. Clearly the ârandomiseâ effect is being called on every load/postback of the page.

Though Iâm savvy enough to, say, write a stored procedure to generate a separate randomised SQL table on a scheduled basis and using that instead, it seems like a sledgehammer to crack a nut.
Iâm guessing there must be some way of retrieving the 60+ records (4 brief text fields each) then storing them in a randomised way âlocalâ to the user, so that paging back and forth maintains the sequence.
Despite trawling the web, Iâve not come across anything that has helped. Paging- yes, randomising â yes. But not both together.
Either thereâs something simple and obvious Iâm missing, or this truly is a tricky puzzle.

Iâm not looking for someone to write the code/markup for me, simply to suggest what approach is needed and, perhaps, where I might find reference material to help me put the code together.
The software/architecture I use includes MS Expression Studio 4 Web Professional, Visual Studio Express 2012 for Web, SQL Server 2008 and ASP.NET 4.5 with VB.

Phil.

Imar · April 25th, 2013, 03:09 AM

Hi Phil,

You could store the data retrieved from the database in a user specific store such as session state. On the first request, you get the data from the database and store it, on subsequent requests you get the data from session state instead. If the data you need to access is large, you could store the unique IDs of the sorted data in session state and use that to retrieve more data on further requests.

For this to work, you need to write some custom code. Rather than using a SqlDataSource control, you need to write your own code using, say, the Entity Framework to get your data out of the database and store it in session state.

Does this help? Let me know if you want to see some "pseudo" code to make this work.

Cheers,

Imar

pjskeldon · April 25th, 2013, 10:43 AM

Thanks Imar - that was quick!

I've not used the Entity Framework before, so let me do a bit of reading around first. If I'm still stumped I'll ask you for that pseudo-code.

Again, many thanks. Your books have helped me pick up ASP.NET in just a few weeks!

Regards,

Phil.

Imar · April 25th, 2013, 11:09 AM

>> Your books have helped me pick up ASP.NET in just a few weeks!

If you have the 4.0 or 4.5 version of the book, there's a whole chapter devoted to EF.

Cheers,

Imar

Robinmarsh321 · May 6th, 2013, 03:06 PM

I like to lean more towards #4 as well because if we use flat-files, we will take the same performance hit as a cron job, but the flat-file guarantees that every time the pre-generated list is generated, a user will feel that performance hit, whereas a cron job will do it in the background, and for a user to feel that performance hit, they'd have to enter the site at that exact moment that database is being updated

pjskeldon · May 8th, 2013, 08:07 AM

Thanks for your responses. I've been enjoying something rare in Britain lately - some sunshine. Now I'm back on this!

Imar - I do have your '4.5' book so will read up on EF this afternoon and try it out. Though I've stripped the page down to the bare essentials, everything else I've tried so far has failed to crack this one, including VB to retrieve and bind the data in a DataTable on initial page load (as suggested by the Wrox 'Professional ASP.NET 3.5' book). It gets the data but then the paging doesn't work - advert images remain static, although the buttons 'work' as if (behind the scenes) it really is paging the data.

Rolling up my sleeves...

Phil.

barbarahambly · May 8th, 2013, 08:49 AM

When a user comes in and clicks on the link, the items on the page should be randomized. As the user clicks on page two, three onwards, it should follow the same random pattern that it generated the first time so that when I go back to the first page the items on that page would be same as when the user first clicked on the link.

Imar · May 8th, 2013, 01:40 PM

Let me know if you get stuck and I'll try to cook up an example for you....

Imar

pjskeldon · May 8th, 2013, 02:30 PM

Thanks Imar.

I'm taking this slowly as I'm new to this.
Not only that but the original website was developed using Expression Studio 4 Web Professional. That doesn't seem to like recent ASP.NET syntax (perhaps limited by it being an older product) so I'm porting the whole thing to Visual Studio Express.

Of course in doing that I need to learn a new product (more time!) and, if I use any new features on ASP.NET, I'll need to migrate the website to the 4.5 model. I know the WEB.CONFIG is different and I've been reading up on using VS to do the transformation for me.

All in all, some work ahead of me! You can see why just setting up a stored procedure to create a daily random table seemed so attractive.

But then I wouldn't have bought so many books and wouldn't have learned anything new!

Now if only I could use COBOL...

Phil.

Imar · May 9th, 2013, 05:43 AM

Quote:

All in all, some work ahead of me! You can see why just setting up a stored procedure to create a daily random table seemed so attractive.

You could still do that and call it from custom code or EF.

But I thought you needed to randomize on "every visit"?

Imar