Q:

Automapper, add number of days to destination DateTime property

I'm have a scenario where I am trying to map an integer value in my source object to a DateTime property. Naturally you can't do that. But what I want to do is add the amount of days in the integer in my source, to the DateTime property value of my destination property.
I haven't been able to find a solution so far that explains this scenario.
Anyone know how to do that ?
Pseudo code example:
Mapper.CreateMap<EditAdView, Ad>()
         .ForMember(dest => dest.ExpirationDate, opt => opt.MapFrom(src => dest.ExpirationDate.AddDays(src.ExtendedDurationInWeeks * 7)); 

The above example doesn't work, but it does show what I want to do. Namely add an amount of days to the existing value of the destination property object
Keep in mind: the dest.ExpirationDate property is already populated with a value, which is why I need to update it from my source object.
Thanks in advance.
Solution: (see below answer for details)
       //in the mapping configuration
       Mapper.CreateMap<EditAdView, Ad>()
              .ForMember(dest => dest.ExpirationDate, opt => opt.Ignore())
              .AfterMap((src, dest) => dest.ExpirationDate = dest.ExpirationDate.AddDays(src.ExtendedDuretionInWeeks * 7));

       //in the controller
       existingAd = Mapper.Map(view, existingAd);

A:

I think this will do what you're looking for:
public class Source
{
    public int ExtendedDurationInWeeks { get; set; }
}    

public class Destination
{
    public DateTime ExpirationDate { get; set; }

    public Destination()
    {
        ExpirationDate = DateTime.Now.Date;
    }
}

var source = new Source{ ExtendedDurationInWeeks = 2 };
var destination = new Destination {ExpirationDate = DateTime.Now.Date};

Mapper.CreateMap<Source, Destination>()
      .AfterMap((s,d) => d.ExpirationDate = 
                        d.ExpirationDate.AddDays(s.ExtendedDurationInWeeks * 7));

destination = Mapper.Map(source, destination);

