[PyQt] use dip with a classic parent child relationship

[John Fabiani]

Hi,
I have reviewed the doc's and the examples (well at least once).  So far 
it looks like alot of the automatic stuff is done and lot's of ways to 
deal with making changes.

But I don't see the an example of the classic parent ->childl 
->grandchild model.  The standard invoice header with invoice line items 
where there are two tables used.
How is that done?  I did not gather the info from the doc (or I missed it).

Johnf