Exceptions

The Automapper currently can throw a single type of exception (the DuplicateMappingException) under two different circumstances: -

###You have multiple concrete types that implement the same interface. e.g.

         public interface IMyService { }
         public class MyService : IMyService { }
         public class MyOtherService : IMyService { }

With the default behaviour of the Automapper, it expects to find one and only one implementation of a given interface.

How do I fix this?

You have several options: -

1. If you intend to only use one of these implementations at runtime, mark the other one with the [DoNotMap] attribute (or fluent equivalent).
2. If you want to access all implementations at runtime, either: -
   • Mark the interface as a [Multimap] (or fluent equivalent)
   • Use the MultimapByDefault mapping behavior when calling the Automapper. See here for more details on Multimaps.

###You have multiple concrete types mapped with the same named registration. e.g. public interface IMyService { } [MapAs("Foo")] public class MyService : IMyService { } [MapAs("Foo")] public class MyOtherService : IMyService { }

Unity will simply overwrite named registrations with the latest one it gets (kind of a "last past the post" behaviour). To prevent accidentally missing mappings, if the Automapper finds two mappings for the same interface with the same name, it throws an exception.

How do I fix this?

1. Change the explicit named mapping to something else.
2. Use the implicit MultimapByDefault behaviour, which will automatically generate registration names based on the concrete type being mapped.