While implementing AutoMapper in some existing code, I came across the need to map to a nullable property. Other business logic relied on this particular long being null instead of 0. The DTO has a property that contains a (long)Id, but the Entity contains the virtual property as well as a nullable long? of the Id. Anyway after fumbling through a few tries, I finally came upon the solution and wanted to share it here.

In the MapperProfile for the direction of DTO to Entity you have to do a null check, but the trick for me was having to explicitly cast to (long?)null.

CreateMap<ExampleDto, ExampleEntity>().ForMember(ee => ee.ExampleId, options => options.MapFrom(ed => ed.ExampleProperty != null ? ed.ExampleProperty.ExampleId : (long?)null)).NoVirtualMap();

Hope someone else finds this helpful, and finds it here.

    • zeroadam@programming.devOP
      1·
      1 year ago

      I can certainly test this. My question would then be, will this result in actually mapping a null in the dto, or would the .ExampleProperty? just “be null” and cause the long property to instantiate to 0?

      • dbilitated
        1·
        1 year ago

        i’m pretty sure it’ll be a long? - did you try it?

        • zeroadam@programming.devOP
          1·
          1 year ago

          So… When I change…

          .ForMember(ee => ee.ExampleId, options => options.MapFrom(ed => ed.ExampleProperty != null ? ed.ExampleProperty.ExampleId : (long?)null))

          TO:

          .ForMember(ee => ee.ExampleId, options => options.MapFrom(ed => ed.ExampleProperty?.ExampleId))

          I am presented with: CS8072 - An expression tree lambda may not contain a null propagating operator.