Quite often, I'm being asked to provide an option for cascading drop-down lists that also filter based on the selections made by the user on the previous drop-down list. A few examples when this could be asked are filtering countries based on region selected, filtering schools based on district, filtering departments based on divisions, filtering parts based on model vehicle, and many more.

I'm going to give an example for region and country. You can replace this with any other options that fit your needs.

You are going to need the following:

- 2 custom lists (one of the region and another one for the country)
- Document library or list that will use the 2 custom lists mentioned in the bullet above
- Document library where to save your code to
- jQuery (you can download it from here: http://docs.jquery.com/Downloading_jQuery)
- SPSServices jQuery (you can download it from here: http://spservices.codeplex.com/releases)

I managed to make it work using jquery-1.8.1.min and jquery.SPServices-0.7.1a.min. You may want to try other versions if it doesn't work for you. Sometimes it's a bit of trial and error, like with many SharePoint things.

1. Download the two files and upload them to a document library in SharePoint of your choice and to which you have permissions over in the site;

2. Create the first custom list. In the example, I'm going to name it lookupRegion. Then I'm going to modify some settings, such as removing the ability to attach files, as well as adding a description ("This is the region name") and enforcing unique values for the Title column. Then I'm going to add a few values in there:
3. Create the second custom list. In the example, I'm going to name it lookupCountry. Then I'm going to remove the ability of attaching files (in the list settings) and then I'm goint to make some changes to the Title column, as well as create a second column, as follows,

Title: Add a description ("This is the country name") and enforce unique values;
Region: Create a region column; this column is a lookup column to the Title field in the lookupRegion custom list and it is a required column (you want to make sure that a region is provided).

4. Add a few values in this list:
5. I will now create a Regional Files document library (you can create a list if not) and I will create one column named Region (lookup column to the lookupRegion list Title column) and another column named Country (lookup to the lookupCountry Title column.)
6. Using Notepad, create a file and type in the following:

<script language="javascript" src=" /URL_to_your_code_location_on_your_SharePoint_site/jquery-1.8.1.min.js"></script>

<script language="javascript" src=" /URL_to_your_code_location_on_your_SharePoint_site/jquery.SPServices-0.7.1a.min.js"></script>
<script language="javascript" >

$(document).ready(function() {
relationshipList: "lookupCountry",
relationshipListParentColumn: "Region",
relationshipListChildColumn: "Title",
parentColumn: "Region",
childColumn: "Country",
debug: true


Note: Replace the text in blue above with the URL to the location of your files on your SharePoint site. I prefer to use absolute URLs.

7. Save the file under the name of cascadingdropdown.js (this is very important).

8. Upload this file to the same library where you saved your other jQuery files, or to any other library of your choice.

9. Go back to the Regional Files document library and select Default Edit Form from the Form Web Parts icon in the Customize Library section of the ribbon.
10. Insert a Content Editor Web Part to the page. Edit the web part, give it a meaningful name, remove the chrome, and select hidden in the Layout section. Then reference to the cascadingdropdown.js file (in the Content Link section of the tool pane.) Apply your changes and save ([OK]) the web part. Save and close the page.

11. Upload a file and see if it works. The image below shows that it works for me.
Some last explanations about the parameters used:

relationshipList: This is the name of the list where we have kept the relationship (in our example, lookupCountry);
relationshipListParentColumn: This is the parent column (Region) in the relationship list (lookupCountry);
relationshipListChildColumn: This is the child column (Title) in the relationship list (lookupCountry);
parentColumn: This is the parent column (Region) in the library (or list) where we want to implement this (Regional Files);
childColumn: This is the child column (Country) in the library (or list) where we want to implement this (Regional Files).
For some reason that Microsoft probably only knows, you cannot create lookup columns to Choice columns within other custom lists. Lookups seem to only work on Single Line of Text type of columns, which doesn't make much sense to me. However, there is a work-around using Calculated values.

I discovered this once when I was trying to add a lookup column pointing to a very extensive list of countries, and a few other things, such as regions, divisions, etc.

The purpose of using Choice columns is for most part to force the user to make selections from a predefined list, so as to avoid duplicate values or mispellings.

Why would Microsoft not allow pointing lookup columns to choice columns is beyond me. But well, let's dive in the work-around I found. By the way, this works for both MOSS 2007 and SharePoint 2010.

So the first thing we need to do is create a custom list where to host the Choice column.
As you can see in the example image to the left, I've created the Country column as a Choice column.

The next step is to create the column that will actually be used for the lookup. I'm going to call this column LookupCountry.

I'm going to designate is a Calculated value column. And then I'm going to insert the Country column.

The next thing you need to do is determine the data type that will be returned from the column. For my example, I'm good using Single line of text; therefore, I won't change the default value suggested by SharePoint.

So now we need to go to the second list, from where we want to reference the list of countries.

Create a new column on this second list and select Lookup as the type of information.

Make any additional selections you may need (such as whether to require that this column must contain information).

Select your first custom list, the one where you created the calculated value column at the Get information from drop-down list.

And then select the Calculated value column from the list (where it says In this column).

Save everything and voilá! Once some values are input in the first list, the lookup drop-down on the second list should display some values.