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I wouldn't go with a constructor, but you could create a static method on the subclass (if you cannot alter the base class) that creates the ItemDetailViewModel from Models.AssetItem like this:

public static ItemDetailViewModel Create(Moddels.AssetItem model)
{
    var config = new MapperConfiguration(cfg => cfg.CreateMap<Models.AssetItem, ItemDetailViewModel>());

    var mapper = config.CreateMapper();

    return mapper.Map<ItemDetailViewModel>(model);
}

or you can create an extension method on the base class doing the same.

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