Model does not implement INotifyPropertyChanged

In the context of the MVVM pattern, how to structure the ViewModel when the models don't implement the INotifyPropertyChanged interface?

I like to keep my models as simple as possible and to implement the INotifyPropertyChanged interface just for binding purposes seems like an unwanted complexity. So in most cases I require my VMs to wrap model properties like in the following example:

class ViewModel : INotifyPropertyChanged
{
    private Model model;

    public int MyProperty
    {
        get { return model.MyProperty; }
        set
        {
            if (value != model.MyProperty)
            {
                model.MyProperty = value;

                // Trigger the PropertyChanged event
                OnPropertyChanged("MyProperty");
            }
        }
    }

    /* ... */
}

      

        
        
        
      

    

This will make the bindings work fine, including double-sided.

Now, what happens if the command executes a model method with complex logic (affecting the value of many properties of different objects)? The model does not implement INotifyPropertyChanged, so we cannot know that it has been updated. The only solution that comes to my mind is to use messaging (mediator pattern) to inform all VMs about the execution of the method so that each VM fires a PropertyChanged event for every potentially affected property:

// Sample ICommand.Execute() implementation
public void Execute(object parameter)
{
    var model = (Model)parameter;

    model.VeryComplexMethod();

    // Just an example, the string "VeryComplexMethodExecuted" is
    // sent to all listening VMs. Those VMs will in turn fire the
    // PropertyChanged event for each property that may have changed
    // due to the execution of the complex model method.
    Messaging.Broadcast("VeryComplexMethodExecuted");
}

      

        
        
        
      

    

Share your ideas, thanks.