How can I use Automapper to map an object to an unknown destination type?

Question

Consider the following scenario. I have a number of classes that share a common base class and I have defined an automapper mapping for each derived class. Something like this:

class A : Base {}

class B : Base {}

class ContractA : ContractBase {}

class ContractB : ContractBase {}

void Foo()
{
    Mapper.CreateMap<A, ContractA>();
    Mapper.CreateMap<B, ContractB>();
}

So far so good. But now I want to create a method like this:

ContractBase Foo()
{
    Base obj = GetObject();

    return Mapper.???
}

The problem is that all of AutoMapper's Map variants require that I either know the destination type at compile time or have an object of that type available at runtime. This is seriously frustrating since I have defined only one map for each source type. AutoMapper should be able to infer the destination type given only the source type.

Is there any good way around this? I want to avoid creating a dictionary mapping source types to destination types. While this would work, it would mean that I'd essentially have to define two mappings for every source type.

Answer 1

You could access the mappings stored in AutoMapper:

ContractBase Foo() {
  Base obj = GetObject();

  var sourceType = obj.GetType();
  var destinationType = Mapper.GetAllTypeMaps().
    Where(map => map.SourceType == sourceType).
    // Note: it's assumed that you only have one mapping for the source type!
    Single(). 
    DestinationType;

  return (ContractBase)Mapper.Map(obj, sourceType, destinationType);
}