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Business Layer - Data Access Layer - Multiple Drop-Down Lists - ASP.NET

Posted on 2007-11-21
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Hello

I am currently writing a 3 tier application for the first time. After reading a lot about the theory behind it, I am now beginning to implement it. I have various pages where the user makes a selection based on mulitple dependant drop-down lists.

For example if the user were searching for a vehicle:
1st drop-down list: vehicle type (chosen by user: car/automobil)
2nd drop-down list: make (chosen by user: Toyota)
3rd drop-down list: model (chosen by user: Prius)

hence whatever the user chooses in the first drop-down list, then populates the 2nd drop-down list, and so forth.

How would I implement this on the webpage and in the business / data access layers? Ideally the page would not reload after the selection has been made on a drop-down list.

Any ideas?
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Question by:riffrack
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SQL_SERVER_DBA earned 1400 total points
ID: 20328366
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Expert Comment

by:Jens Fiederer
ID: 20328377
This has very little to do with the business/data access layers - except that this is where you get your data from.

The reloading of the page is entirely a matter of Presentation - your UI layer.

With classic Web programming there is no way to do this without either prefetching ALL the data, or reloading the page.

With AJAX, you do not reload the page, you simply request additional information for the current page.
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Assisted Solution

by:surajguptha
surajguptha earned 600 total points
ID: 20328389
1) I guess all the models/ cars/ makes would be not a lot of data. You could fetch all of it on form load and use javascript to show the relevant make for a car

2) You could design two middle tier functions that take vehcle and return all makes and take one make and return all models. You could use ajax in this case to make sure that the page is not posted back after the dropdowns are selected
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Author Comment

by:riffrack
ID: 20329712
Thanks SQL Server Dba.....that solves the drop-down list issue.

This application is fairly small & most the interaction will be between the db and the website. Not much validation, as the user is quite limited.

My question related to the business logic refers to the case that I have a webpage with multiple drop-down lists & a database table. How do I get these 2 parts to optimally communicate in a 3-tier approach?
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LVL 10

Expert Comment

by:Alpesh Patel
ID: 20329993
Your requirement is just nothing but a synchronisation of   AJAX , UI and Web Service and DataBase.

here,

UI is your 1st tier
Webservice is your 2nd tier same the business layer
DataBase is your 3rd tier.

now from your discription i guess that u are new for web applicaitons so u must be awair  with the webservice

here your webservice would have that webmethods which gives u data for that 3dropdown
and

you can just call that method to filled up that dropdown on perticular event
means.

-- on the selectedchange event of the 1st dropdown.. fill up the second one
-- on the selectedchange event of the 2nd dropdown.. fill up the third one....... and go on............

i think this above discription will give u clear view how to use business layer and synchronise your UI for that....

now u want one more thing to do is that u dont want to reload the page on each selctedchange event of dropdown...... for that u have to use AJAX

now for AJAX u have to download AJAX free framework and install it on your computer .... u can do it from
http://www.asp.net/ajax/

now as u create webapplication from studio 2005, u have to create AJAX based webapplication, which u can get option in new application wizard, or u can get study from the video tutorial  http://www.asp.net/learn/ajax-videos/

get the study of AJAX application and make your above application AJAX based
u can also convert your existing asp.net applicaiton in to the AJAX base asp.net application.

if u need anyting more u can knock me.

thanx and regards


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Author Comment

by:riffrack
ID: 20340468
Thanks all of you for your help. I have used the cascading drop-down lists from the ajaxControlToolbox & have used a middle tier to acces the data.
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