Where to place AutoMapper.CreateMaps?

Doesn’t matter, as long as it’s a static class. It’s all about convention.

Our convention is that each “layer” (web, services, data) has a single file called AutoMapperXConfiguration.cs, with a single method called Configure(), where X is the layer.

The Configure() method then calls private methods for each area.

Here’s an example of our web tier config:

public static class AutoMapperWebConfiguration
{
   public static void Configure()
   {
      ConfigureUserMapping();
      ConfigurePostMapping();
   }

   private static void ConfigureUserMapping()
   {
      Mapper.CreateMap<User,UserViewModel>();
   } 

   // ... etc
}

We create a method for each “aggregate” (User, Post), so things are separated nicely.

Then your Global.asax:

AutoMapperWebConfiguration.Configure();
AutoMapperServicesConfiguration.Configure();
AutoMapperDomainConfiguration.Configure();
// etc

It’s kind of like an “interface of words” – can’t enforce it, but you expect it, so you can code (and refactor) if necessary.

EDIT:

Just thought I’d mention that I now use AutoMapper profiles, so the above example becomes:

public static class AutoMapperWebConfiguration
{
   public static void Configure()
   {
      Mapper.Initialize(cfg =>
      {
        cfg.AddProfile(new UserProfile());
        cfg.AddProfile(new PostProfile());
      });
   }
}

public class UserProfile : Profile
{
    protected override void Configure()
    {
         Mapper.CreateMap<User,UserViewModel>();
    }
}

Much cleaner/more robust.