I am trying to get my head around caching.

Here is the senario:

I have a messageboard web part on a bunch of cms.news documents to allow users to comment.

In another part of the site I have a repeater with a transformation which shows these documents.

I have a custom function which checks the number of comments on each of these documents to shows in the transformation .

What I would like to know is:

1: do I need to write code in my custom function which caches the MessageBoard object for each of the documents (as below)
2: if so, how do I make sure that the cache is cleared when a new comment is added to a message board on a document

Here's what I have so far:

Custom Function to get number of comments on a document:

public static string GetMessageBoardCount(object documentid, object nodeid, string boardname)
{

BoardInfo bi = null;
//check the cache
using (CachedSection<BoardInfo> cs = new CachedSection<BoardInfo>(ref bi, 1, true, null,"BoardCountCache" , documentid + boardname))

{
if (cs.LoadData)//cache item not found
{

bi = BoardInfoProvider.GetBoardInfo(boardname,ValidationHelper.GetInteger(documentid,0));

cs.Data = bi;

CacheDependency cd = null;

cd = CacheHelper.GetCacheDependency(new string[] { "nodeid|" + nodeid.ToString() });

cs.CacheDependency = cd;

}
}

return bi.BoardMessages.ToString();//count of messages

}

Cheers

Richard