I am getting my knickers in a twist recently about View Models (VM).

Just like this guy I have come to the conclusion that the collections I need to expose on my VM typically contain a different type to the collections exposed on my business objects.

Hence there must be a bi-directional mapping or transformation between these two types. (Just to complicate things, on my project this data is "Live" such that as soon as you change a property it gets transmitted to other computers)

I can just about cope with that concept, using a framework like Truss, although I suspect there will be a nasty surprise somewhere within.

Not only must objects be transformed but a synchronization between these two collections is required. (Just to complicate things I can think of cases where the VM collection might be a subset or union of business object collections, not simply a 1:1 synchronization).

I can see how to do a one-way "live" sync, using a replicating ObservableCollection or something like CLINQ.

The problem then becomes: What is the best way to create/delete items?

Bi-directinal sync does not seem to be on the cards - I have found no such examples, and the only class that supports anything remotely like that is the ListCollectionView. Would bi-directional sync even be a sensible way to add back into the business object collection?

All the samples I have seen never seem to tackle anything this "complex".

So my question is: How do you solve this? Is there some technique to update the model collections from the VM? What is the best general approach to this?