Creating drop down lists on a SharePoint blogging site

Anbu Thangarathinam has posted a version of the cascading dropdowns that allows unlimited siblings.  So instead of a parent and child control there is just one control and you configure whether it will be a parent or a child—Unlimited-siblings.aspx
End Update
Just to clarify the intention of providing these controls and the source code.   This is purely a proof on concept to demonstrate that you can overcome the issue of cascading dropdowns (and many other limitations of SharePoint) by writing your own custom field controls.
It is not intentded that you will just be able to whack this onto a production box and it will solve all of your problems.  You will most likely need to take the code and modify it to suit your needs. 
Dependent Drop Downs, Cascading Drop Downs, Filtered Drop Downs.  Whatever you want to call them, this is where you have a secondary drop down list filtered based on the choice from the primary drop down list.  For example:  select a country and you get another drop down list populated with the cities in that country.
This functionality doesn’t seem to be there in WSS 3.0 and/or MOSS 2007. Perhaps I am missing something?  (It wouldn’t be the first time)  But this seems to befundamental functionality.   Here is some more detail on the scenario:
Country List: I just want a basic drop down list of countries:

City List: I want to filter the cities based on the selected country:

I want a cascading or filtered drop down like so (select Australia, and get a list of Austrlian cities):

Select Germany and get a list of German cities: 
Anyway, I couldn’t find a way to do this out of the box, so…I decided to create my own custom field controls to overcome the problem.
I found a couple of useful articles on writing custom field controls.  This article describes how to create a custom drop down list user control along with a custom property page:
I used a lot of code from this example, which has a couple of interesting points.First of all it shows how to create a custom Choice field that can be populated from any list on any site on the web farm (not just the current site). It also has an example of a way to get around the problem of saving custom properties of field controls. For some reason this is not as easy as it should be. I think this will be fixed in SP1. This article describes this problem: aaronrh/archive/2007/05.aspx
Instead of using a delimited string, I used a class to temporarily store the property values. Here is what my property pages look like for the Parent and Child drop down lists:

Anyway, after learning how to overcome the challenges of field controls in general, it was time to move on to the bigger problem of finding a way to create cascading drop downs. I figured there was hope in the “cross list query” or “caml query”: us/library/ms467521.aspx
For example, if I want to filter a list of cities based on a country field in that list:
string caml = @””
SPQuery query = new SPQuery();
query.Query = string.Format(caml, “”Country””, “”Australia””);
SPListItemCollection results = list.GetItems(query);
this.ChildDropDownList.DataSource = results.GetDataTable();
this.ChildDropDownList.DataTextField = “”City””;
this.ChildDropDownList.DataValueField = “”City””;
So I have a parent drop down list that has a SelectedIndexChanged event, that I use to call a method in the child control that binds to the results of the above query.
void ParentDropDownList_SelectedIndexChanged(object sender, EventArgs e)
     ChildDropDownListFieldControl child = (ChildDropDownListFieldControl)
               FindControlRecursive(this.Page, “”ChildDropDownList””).Parent.Parent;
I played around with a lot of different ways to locate the Child drop down list on the page. This is the only one I got to work. (There has to be a better way?)
Anyway, I would appreciate any feedback on any better ways to do this. Here is thesource code; I also have asolution file that you can use to install the controls. Just edit the install.bat and point it to the WSS or MOSS site you want to install it on.


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