Question

Consider these 3 simplified example types I pass up and down (I actually only automap between DomainObject and WrapperClass though):

public class DomainObject
{
   public int Prop1 {get;set;}
   public int Prop2 {get;set;}
   public int ComputedValue1 {get;set;}
   public int ComputedValue2 {get;set;}
}

public class DALEntity
{
   public int Prop1 {get;set;}
   public int Prop2 {get;set;}
}

public class Wrapper
{
   public DALEntity ToFromDB {get;set;}
   public int ComputedValue1 {get;set;}
   public int ComputedValue2 {get;set;}
}

The DomainObject is what most of my application deals with, while DALEntity is what my data access layer deals with when CUDing around with the DB. Notice there are (in this case) 2 computed values that do not get persisted – rather they are computed externally (for this example doesnt matter how). Hence I would rather not include them in my DALEntity.

For mapping upward (src==DALEntity, dest==DomainObject), Id like to tell Automapper that for any field in DomainObject it doesnt know how to populate, “look in this complex property for a property where the name matches”. As I understand it, right now, I need to explicitly specify all the properties manually via MapFrom when I create the mapping. Would be a real timesaver (and less error prone) to be able to specify a kind of “using” statement for how to map.

I guess you could call it “Projection via hint” 🙂

Is this currently possible?

Answer 1

I would move the computation of the computed properties to its own class. You could then use dependency injection and have the computed properties call the injected class to populate themselves. AutoMapper shouldn’t have to know this. The DO should be aware of what it needs to be fully operational, or, barring that, its factory should.

This also would increase the testability of the class.

Anyways, if you still want to go this route you can pass in a function to the mapping method of Automapper.

Something like:

 Mapper.CreateMap<DAL, DO>()
                .ForMember(m => m.CalcProp, 
                           opt => opt.MapFrom(src => 
                            { anon function that calls calculating code, passing src } ));