To map Model classes to ViewModel classes or aggregate Model classes in ViewModel classes

I'm curious as to what people consider better practice, between duplicating model structure in the view model and using a mapping tool to move data between the two, or aggregate the model inside the view model, i.e. have a property on the view mod开发者_StackOverflow社区el class that is a reference to the actual model. Which is considered a better approach in general?

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The "better" approach will always be having a distinct view model for each view, and then using AutoMapper or something similar to handle the guts of the mappings for you

public class MyViewModel
{
  public int Id { get; set; }
  public string Name { get; set; }

  public MyViewModel() { }
  public MyViewModel( MyModel model )
  {
    AutoMapper.Mapper.Map(model, this);
  }
}

It will vary in practice sometimes, but having a distinct, concise viewmodel will offer the most flexibility.