c# - Automapper: complex if else statement in ForMember

Question

Assuming the Date is a nullable DateTime:

Mapper.CreateMap<SomeViewModels, SomeDTO>()               
             .ForMember(dest => dest.Date,
                        opt => opt.MapFrom(src =>
                        {
                            DateTime? finalDate = null;
                            if (src.HasDate == "N")
                            {
                                // so it should be null
                            }
                            else
                            {                                   
                                endResult = DateTime.Parse(src.Date.ToString());
                                
                            }                               
                            return finalDate;

                        }));

The error I got was:

Error 30 A lambda expression with a statement body cannot be converted to an expression tree.

Of course I'm fully aware that I can simplify the query such as:

Mapper.CreateMap<SomeViewModels, SomeDTO>()
             .ForMember(dest => dest.Date,
                        opt => opt.MapFrom(src => src.HasDate == "N" ? null : DateTime.Parse(src.Date.ToString())));
    

But what if I insist to retain the structure of the first example, because I have more complicated if else statements, that the second example will not able to cater for, or at least will not be very readable?

Answer 1

In recent versions of AutoMapper, ResolveUsing was removed. Instead, use a new overload of MapFrom:

void MapFrom<TResult>(Func<TSource, TDestination, TResult> mappingFunction);

Just adding another lambda/function parameter will dispatch to this new overload:

        CreateMap<TSource, TDest>()
                .ForMember(dest => dest.SomeDestProp, opt => opt.MapFrom((src, dest) =>
                {
                    TSomeDestProp destinationValue;

                    // mapping logic goes here

                    return destinationValue;
                }));