I followed the example you gave and my custom filter works (I am using an objectdatasource), but with 3 issues:
1. When the grid rebinds, the RadComboBox display returns to index 0 - it needs to remain on the index the user selected, so if the user selected "pantyhose," the combobox remains at "pantyhose" and does not return to "whips and chains"
2. The example does not give a way out of the filter - once in, you are stuck. How can I get a "no filter" option into the combobox?
3. The note at the bottom of the example ( http://www.telerik.com/help/aspnet-ajax/radgrid-filter-template.html
) surprises those who do not read the release notes (does anybody???) that LINQ syntax is the default (for .NET 3.5) for interpretting the syntax of the embedded SELECT, etc., statements in the presentation tier. I don't understand this at all - how LINQ can be interpretting a database call from data access object. I am not whining; I just don't understand it. I will complain about the lack of references to how RadGrid can now use LINQ, especially LINQ2DataSets and LINQ2XML since most of the civilized world uses Oracle and both M$ and Oracle are in a pissing contest over this issue.
Finally, I can't stand embedding busness rules in the presentation layer!!! How do you access a Rad child control, like the combobox buried in a BoundGridColumn buried in a RadGrid from the server (code-behind)? I have found not a single example or tutorial on this site that explains this. That is not to say it doesn't exist, but it sure must be hard to find. I really do not understand why you guys put your business logic in the web page. Well....I do have some thoughts on that, but they are not nice.