Document library view: Group by a column with multiple values

Question

I have a document library which has a managed metadata column.
I would like to create a view which groups the documents by this managed metadata column.
The managed metadata column can have multiple values.
I know that this is not possible with SharePoint's group by, since it only accepts those columns which can have only one single value.
But is this possible to accomplish by some other means, e.g. Content query web part? Or is there perhaps a 3rd party solution to this?
Is it possible to change the group by settings somehow to allow Group by to function with columns with multiple values? <- this may be far fetched...

Answer 1

Hi Pekch,
I'm assuming you have VS2010 to build the custom web part. From there you will need to figure out the following:
Get a SPList object for the Document Library (See below for code example)
Loop through all the documents in the SPList object 
If you have audience targetting enabled, then you'll need to determine if the user has access to the document by checking the "Target_x0020_Audiences" column)
As you also want to group by metadata, you'll need to populate 2 datatables (one table with a column containing unique metadata values and another table with a metadata column and other document related columns).  Link these two tables via a dataset
relation.
Set the dataset as the datasource for a repeater, add in some css and javascript for the group expand/collaspe and it should be close to what you need.
This will be a time consuming task if you don't know where to start or have problems figuring out how to perform a certain operation.  So you may want to determine if the functionality you want is required or just a "nice to have".  Good
luck and if I have some spare time, I'll create a blog post outlining how to do all the above.
I got the below code from a sharepoint blog sometime in the past and you can use it to retrieve a list.
You can use it like this: GetListByUrl(http://servername/Shared%20Documents/Forms/AllItems.aspx)
using    Microsoft.SharePoint;
public SPList GetListByUrl(string listURL)
SPList list = null;
try
using (SPSite site = new SPSite(listURL))
if (site != null)
// Strip off the site url, leaving the rest
// We'll use this to open the web
string webUrl = listURL.Substring(site.Url.Length);
// Strip off anything after /forms/
int formsPos = webUrl.IndexOf("/forms/", 0, StringComparison.InvariantCultureIgnoreCase);
if (formsPos >= 0)
webUrl = webUrl.Substring(0, webUrl.LastIndexOf('/', formsPos));
// Strip off anything after /lists/
int listPos = webUrl.IndexOf("/lists/", 0, StringComparison.InvariantCultureIgnoreCase);
if (listPos >= 0)
// Must be a custom list
// Strip off anything after /lists/
webUrl = webUrl.Substring(0, webUrl.LastIndexOf('/', listPos));
else
// No lists, must be a document library.
// Strip off the document library name
webUrl = webUrl.Substring(0, webUrl.LastIndexOf('/'));
// Get the web site
using (SPWeb web = site.OpenWeb(webUrl))
if (web != null)
// Initialize the web (avoids COM exceptions)
string title = web.Title;
// Strip off the relative list Url
// Form the full path to the list
//string relativelistURL = listURL.Substring(web.Url.Length);
//string url = SPUrlUtility.CombineUrl(web.Url, relativelistURL);
// Get the list
list = web.GetList(listURL);
catch { }
return list;