Automapper error on simple conversion without CreateMap - asp.net-mvc

Question

I have these 2 models:
public class SiteSettingsViewModel
{
public decimal SubscriptionFee { get; set; }
}
public class SiteSettings
{
public decimal SubscriptionFee { get; set; }
}
and the code:
var model = Mapper.Map<SiteSettings, SiteSettingsViewModel>(settingService.GetSettings());
Which throws the error of:
Trying to map WebApp1.Domain.Site.SiteSettings to WebApp1.WebUI.ViewModel.SiteSettingsViewModel.
Missing type map configuration or unsupported mapping.
Exception of type 'AutoMapper.AutoMapperMappingException' was thrown.
Why do I need to put the code:
Mapper.CreateMap<SiteSettings, SiteSettingsViewModel>();
To me, this seems like I'm writing monkey code. This is not needed.
Why didn't the 1 line work?

Answer 1

One reason is that it's useful for more complex mapping scenarios where you need to define more specific behaviors. For example (from CodePlex):
Mapper.CreateMap<CalendarEvent, CalendarEventForm>()
.ForMember(dest => dest.EventDate, opt => opt.MapFrom(src => src.EventDate.Date))
.ForMember(dest => dest.EventHour, opt => opt.MapFrom(src => src.EventDate.Hour))
.ForMember(dest => dest.EventMinute, opt => opt.MapFrom(src => src.EventDate.Minute));
Another option for simple mapping like what you're doing is to make a generic mapper that takes care of the CreateMap call for you, like this:
public interface IMapper<T1, T2>
{
T1 Map(T2 source);
}
public class Mapper<T1, T2> : IMapper<T1, T2> where T1 : class where T2 : class
{
public Mapper()
{
Mapper.CreateMap<T2, T1>();
}
public T1 Map(T2 source)
{
return Mapper.Map<T2, T1>(source);
}
}
And then you can just instantiate them directly like:
var mapper = new Mapper<SiteSettings, SiteSettingsViewModel>();
Or register them to be injected into your controllers, or wherever else you plan on using them. Hope that helps.