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copied!<p>When I write this kind of software, my VMs never have a reference in any way to the data model. When you couple them like this, you are pretty much married to a simple two-tier solution which can be really tough to break out. </p> <p>If you disconnect the DataContext entirely from your VM and have them live on their own, your application becomes:</p> <ul> <li>Much more testable -- your VMs can be tested without the datacontext</li> <li>Potentially stateless at the data layer -- it's easy to change your architecture to adopt a stateless 3-tier based solution.</li> <li>Able to easily integrate other data sources -- your VMs can elegantly contain aggregates and combinations of other data sources on their own.</li> </ul> <p>So in short, yes, I would recommend decoupling the data access classes from the ViewModel objects throughout the app. It might be a bit more code, but it will pay dividends down the road with the architecture's flexibility.</p> <p><strong>EDIT:</strong> I don't use the change tracking features of the L2SQL objects once they've crossed a distribution boundary. That turns into a can of worms pretty quickly -- you can spend a lot of time with the care and feeding of your data model's object graph inside your viewmodel - which adds not only complexity to the ViewModel, but at least transitively couples the ViewModel to the schema of the database. Instead of doing that, I make the ViewModel pure. When the time comes for them to be persisted, your service layer/repository/whatever does the translation between the ViewModel and the data objects. This at first seems like a lot of work, but for anything other than simple CRUD, this design pays off pretty quickly.</p>

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