ASP.NET server data persistence

Question

Hi,

I'm not really sure exactly how the question should be phrased, so please be patient if I ask the wrong thing.

I'm writing an ASP.NET application using VB as the code behind language. I have a data access class that connects to the DB to run the query (parameterized, of course), and another class to perform the validation tasks - I access this class from my aspx page.

What I would like is to be able to store the data server side and wait for the user to choose from a few options based on the validity of the data. But unless my understanding is completely off, having persistent data objects on the server will give problems when multiple users connect?

My ultimate goal is that once the data has been validated the end user can't modify it. Currently I'm validating the data, but I still have to retrieve it from the web form AFTER the user says OK, which obviously leaves open the possibility of injecting bad data either accidentally (unlikely) or on purpose (also unlikely for the use, but I'd prefer not to take the chance).

So am I completely off in my understanding? If so, can someone point me to a resource that provides some instructions on keeping persistent data on the server, or provide instruction?

Thanks!

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Concrete Example:

We recently hired Inspector Gadget to insert data for the Sign Inspectors who go 'round inspecting the highway signs to make sure none of them have been mangled or stolen by bubble-gum chewing, normally upstanding members of the youth city council.

If Gadget can prove his mettle then he might get promoted to do the actual sign inspections. For now, his only job consists of going to this intranet site an inputing information about the most recent inspections. The district, county, route #, section of road, and dates the sign was installed and inspected.

Of course any of us who were alive in the late 80's are familiar with Gadgets ineptitude. So the site is about as Gadget proof as we can make it. The district/county/route is all filled out through a dropdown list, he only has to manually enter the section start and end and the dates. On occasion he fumbles the mouse and ends out swapping the begin and end of the section, doh! So the text turns red to alert him of the mistake. Unfortunately he chose to wear his anti-red sunglasses today that turn all red colors to black. Well, after attempting to submit the data it shows him an error message telling him where and what he needs to fix. Unfortunately he fat fingered the keyboard and instead of inputting 1.337 he put in 13.37 (miles)- and the road is only 10 miles long! Well, now a message (a modal div) pops up and tells him that the real mileage for the road is 0-10, and that his entry will combine three sections of the road. Then he is given three buttons to choose from. Cancel, which allows him to go and modify his data, Constrain, which will convert 13.37 to 10, and Override which will allow him to input that data anyway.

"Yowza!" Gadget exclaimed, and clicked cancel to go back and fix his mistake. Well the next set of data he input correctly, so a confirmation message popped up showing him the changes he was about to make and asking if it was OK to continue. Well, unfortunately Inspector Gadget knocked over his coffee cup, scattering detritus across his desk. In his haste to clean it up, he clicked "OK", but not before his Go-Go-Gadget electro-magnet accidentally flipped a few bits on his computer, changing the county in the form from ARKANSAS to AKRSANAS, doh!

Had the data been stored on the server across campus, and the only information passed was "OK" or "Cancel", this would have been avoided.

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Of course I can always validate again after the "OK", but it just seems like a hacky workaround.

Anyhow, I hope this clarifies!

Answer 1

I think you are thinking about using the webserver's cache. In ASP.NET, you can use Context.Cache to store data on the server. Once one user cache's it, any other user on the server can also access it.

Since the data is cached on the server, you want to clear the cache everytime you call an update query on the DB. Then the next time you load the data, you can save the data in cache again.

In your select method, check if your Cache[key] is not null. If it is, then load the data from the DB and then save it to Cache[key] before you return the data. If it's not null, then simply load it from the cache instead of the DB.

The key that you use can contain your parameters so you don't have to filter the data from cache....or the key can just be generic so it stores all your data. Then you can a perform LINQ query on the data to filter for your parameters

I hope this is helps.

Answer 2

I think you are referring to Concurrency. Check out the link to get started on understanding it, if that is what you are asking about. You will probably have to do a little more research depending on your back end and your specific situation. Again, if this is what you are looking for you may be particullary interested in pessimistic concurrency.

http://en.wikipedia.org/wiki/Concurrency_control

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EDIT: After reading your example....it sounds like you may want to do the following, good luck.

1. "lock" the record using a pessimistic concurrency pattern of some kind (on the db since that is where the data actually is) when it is accessed by the user inputing the data. This is like making the db record read only.

2. When the user hits ok you would probably have to validate through asp.net code, and if validation is passed, update the db and unlock the db record.

3. If the user hits cancel, don't update the db record, just unlock it.

4. If the user wants to force the input, then just update the db and unlock the db record.