Use ASP.NET AJAX Cascading Drop Down Control to Access a Database

I need cascading dropdownlists for my current project. My database hierarchy structure is designed to have an unspecified indent level. So I might need 3 dropdownlists.. maybe 4, maybe just 2.

Thanks for the introduction :-)

That's an interesting scenario.

I don't have any code that does this, though I'll put it on my list.

Dynamically Adding conrols in ASP.NET somewhat difficult becuase the added controls are not added to any page state mechanism.

You certainly can inject additional DropDowns programatically into the page but you'll need to recreate those additions in the page_init method so postbacks don't remove them.

Joe,

I don't quite understand about this tool needs to use Web Service to pick up data from database. How come this extender doesn't provide DataSourceID attributes to just call the SQLDataSource control to get the data feed instead of going through so much coding with Web Service?

I just think this AJAX control is just making developer to create more codes rather than simplify the coding process for having a cascading dropdown control. We can have a series of cascading dropdown controls by using SQLDataSource wrapped inside the UpdatePanel control, why would we need this AJAX one which requires us to go through Web Service to get data from the database.

Please correct me if I am wrong.

Thank you,

Erik

I liked this video a lot man, thanks a lot dear Joe. You have used a lot of techniques in this video, and it was so benificial to watch it. Thanks a lot man

I do share the same opinion with edirgaria, although maybe I didn't really get the essence. Can you please list the advantages (disadvantages) of using this technique over the UpdatePanel one?

Thanks

Radu

Hi Joe

Very very good video.. this has helped me alot.

But i need to know one thing. What if the javascript is turned of the ajac-cotrols doesn't work!!!!

How do I handle so the page works as standard aspx if javascript is disabled. Are there any examples on that??

There are a couple of reasons for using service methods instead of UpdatePanel.

1.) UpdatePanel is WAY less efficient since it does a complete page postback and executes the complete .aspx pafe lifecycle.

2.) YOu can execute much more server side logic than a simple parametric database query.

As to JavaScript.....

If the user doesn't have JavaScript enabled then there is no AJAX. You need to post back after every selection (which you can't do automaticaly since there is no JavaScript) and build an updated page each time.

What you are saying is that I should also write code in the server-side(aspx.cs) in the load_event that retrives data from the database.

But what if javascript is enabled. It retrives data two times.. one from the Load_event(Serverside) and the secondtime it gets from the Servicefile(constructed for AJAX-controls)????

Thanks

You asked what to do it Javascript was turned OFF.

If JavaScript is on then you just do ASP.NET AJAX.

yes that is what Iam asking for. How do I check if javascript is on so I can use ajax? Iam using services like your example.

Why are you not creating a video on how to detect javascript?? is it not important? Cause I have asked and searched, havent found any good information...

No need for a video.

Just use the code here:

www.codeproject.com/.../Javascript_Detection.aspx

Hi Joe,

I'm trying to implement Cascading DDLs with DB using  Categories and Products tables of Northwind db.

I've two DDLs - category & products and 2 CCDs - ccdCategory and ccdProducts.

I'm getting [Method Error 500] when page loads.

I'm using Web Developer 2005 Express Edition.

Can you please tell me why this happens?

But web service is working correctly.

Hi Joe,

I saw your vedio and was trying to implement Cascading DDLs with DB using  Categories and Products tables of Northwind db.

I've two DDLs - category & products and 2 CCDs - ccdCategory and ccdProducts.

I'm getting [Method Error 500] in Category DDL when page loads.

I've set ServiceMethod & ServicePath properties correctly.

And also the required attributes in web service file.

I'm using Web Developer 2005 Express Edition.

Can you please tell me why this happens?

But web service is working correctly.

Hi joe,

I never thought that implementing ajax in .net is soo easy and interesting.Ya Microsoft makes every thing powerful and easy to implement.I m proud of Microsoft.

And Joe all ajax videos posted by u are just fantastic.

This will help many.Thank u very much.

can u tell me difference between "Atlas" and "Ajax Extension 1.0". Which one should i install to use??

waiting for reply.............

Many THANKS !

I's so rewarding when folks are able to learn from the work I/we do.

BTW - Atlas was just the project name that we used before we released. You should be using the "ASP.NET Extensions for AJAX 1.0".

To Jnaneshwar: You're seeing a 500 Server error ?

Ths is useually an error in the Web Service code and can be seen if the Service Class is not decorated with the ScriptService attribute.

I had a look at AutoComplete Extender, Which OnTextChanged is returning some values in a list box, I want that to be checkboxlist to enable multiple selections. How can that be done

Could I populate a checkbox list with the last cascading drop down list using this method?  I need two drop down lists and one checkbox list for a user to make selections.

Not as it exists now, but since it's open source you could fork your own version of the control.

Joe: terrific example. One question: once these controls are set up and a page postback is done (after completing the rest of the selections on a page), the viewstate of the dropdown list controls seems to get lost. I have seen some references to doing some work OnInit to preserve viewstate, but if the access to the database is all being handled through the extender control properties and a web service, there is not a lot being done that could be moved to "OnInit". Is there a way to preserve viewstate for the cascading dropdowns when returning after a page postback?

Thanks, Walt

Dear Joe,

I'm totally new in AJAX, from this video, I would like to know the code:

Public Fuction GetMakes(byval knownCategoryValues as String, ByVal category As string) As CascaddingDropDownNameValue()

'implementing

End Function

1) Is that the knownCategoryvalues is the reserve word?

2) the function is pass in 2 parameters from where?

3) from the implementing part, the makesValues.add () NewCascadingDropDownValue (row("...").tostring(), row("...").tostring())

the carId return parameter is to pass in to the cascading model's as knownCategoryValue?

4)from the next webmethod: Model

stringDictionary is used when we need to get parameter from parent control? for database?

5)what is that means by Cascadingdropdown.ParseKnownCategoryValuesString(knownCateg oryValue)?

6)if my MakeID is a string value,in the if method, i should put "...or (Not char.tryParse(kv("Make"),makeID)) Then ..."

Hope to hear you soon.Thank you

from the movie above, i would like to know more details about it. Since i'm totally new to ajax,I am so hunger for that...

1) the knowCategoryValues a parameter that sent from where? Shall we use another name to replace it?

2) the string dictionary is act like an abstract table to get values knownCategoryValues from the parent control?

3)instead of use integer as a makeID, I use string as my make ID, then may i write "...Or (Not Char.TryParse(kv("SupplierID"), suppID))) Then ..."?

Hope to hear reply from anyone of you. Thanks.

Y i'm not able to leave a comment here?

METHOD 500 really makes CascadingDropDown a bad thing.

I have wasted to much time trying to trouble shoot this.