Here is the problem:

I'm using relativity module and using views to do node listings of NodeType-A

NodeType-A (parent)
NodeType-B (child)

I want to filter the NodeType-A based on Child count (i.e only show NodeType-A when Count(NodeType-B) == 0)

Since i'm not a drupal guy, i have no idea of how to write : add a dynamic field/column which is not in database, as well as write a filter against that column to filter the data. I've looked at other modules, views manual pages and couldn't figure it out. I would appreciate if somebody help me with this one.

FYI: I'm trying to add the fields and filters to the view file relativity_views.inc that ships with relativity.module

I would really appreciate if someone write a fairly simple example with just one dynamic field for e.g 'child_count' which is not in db, and show the following:

$tables['tablename'] declaration
$fields
$filters
$sorts

Thanks in advance.