One of the biggest headaches when using AutoMapper is making sure to bootstrap all of your CreateMap<TSource, TDestination>() maps for it to work properly. One alternative is to go with ValueInjecter, a convention-based mapper that doesn't require map definitions. I've also seen plenty of code that calls AutoMapper.Mapper.CreateMap in static controller constructors. Recently I was chatting with a web architect who had the opinion that AutoMapper is evil, and he sent me an AutoMapperHelper class he uses. I replied with my approach, and discovered he had never used the AutoMapper.Profile class.

Here is how it works. You just create a class that inherits from AutoMapper.Profile, override the void Configure() method, and call this.CreateMap<TSource, TDestination>():

public class MyCustomWidgetModelProfile : Profile
{
    protected override void Configure()
    {
        this.CreateMap<WidgetEntity, WidgetViewModel>()
            // do all of your custom resolving here
            .ForMember(d => d.ViewOnlyProp, o => o.Ignore())
            .ForMember(d => d.CustomProp, o => o.ResolveUsing(s =>
                new CustomType { s.Prop1, s.Prop2 }))
        ;
    }
}

Then, instead of calling the static AutoMapper.Mapper.CreateMap method, all you have to do is add an instance of this Profile class to the AutoMapper.Mapper.Configuration:

protected void Application_Start()
{
    // among other things,
    AutoMapper.Mapper.Configuration.AddProfile<MyCustomWidgetModelProfile>();
}

This does not get rid of the headache, since you still need to invoke AddProfile once for each CreateMap that needs to be bootstrapped. However with a base class to define all of our CreateMap code, it is much easier to use reflection and scan to find all of that code.

To get rid of the headache, install the AutoAutoMapper nuget package in your app. You can register all of your AutoMapper.Profile implementations with this single line of code:

AutoAutoMapper.AutoProfiler.RegisterProfiles();

By default, this will scan the assembly where it is called from. For small projects with only one assembly, this is all you need. However if you have AutoMapper.Profile classes defined in a different assembly, or spread across multiple assemblies, you can use the RegisterProfiles() overloads that take Assembly arguments. One overload allows you to pass each assembly as a separate argument:

AutoAutoMapper.AutoProfiler.RegisterProfiles(
    Assembly.GetAssembly(typeof(SomeProfileClassInAssemblyA)),
    Assembly.GetAssembly(typeof(SomeProfileClassInAssemblyB)),
    ...
    Assembly.GetAssembly(typeof(SomeProfileClassInAssemblyN))
);

If you prefer to have all of your Assembly instances stacked up before invoking RegisterProfiles, there is another overload that takes only a single parameter:

IEnumerable<Assembly> assemblies = new[]
    {
        Assembly.GetAssembly(typeof(SomeProfileClassInAssemblyA)),
        Assembly.GetAssembly(typeof(SomeProfileClassInAssemblyB)),
        ...
        Assembly.GetAssembly(typeof(SomeProfileClassInAssemblyN)),
    };
AutoAutoMapper.AutoProfiler.RegisterProfiles(assemblies);

The ASP.NET team has also recognized the need for better organization of bootstrap code, and adopted a new App_Start folder which you can see in action by creating a new default MVC4 project. With this approach, you have separate classes that deal with separate concerns in the App_Start folder. For example, the default template has a BundleConfig class, a FilterConfig class, a RouteConfig class, etc. Static methods on these classes are invoked during Application_Start to avoid cluttering the Global.asax:

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();

    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    RouteConfig.RegisterRoutes(RouteTable.Routes);
    BundleConfig.RegisterBundles(BundleTable.Bundles);
}

By default when you install the AutoAutoMapper nuget package, it will add a new AutoMapperConfig.cs class to the App_Start folder of your project. It is your responsibility to wire this up by placing the following line in your Global.asax file's Application_Start method:

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();

    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    RouteConfig.RegisterRoutes(RouteTable.Routes);
    BundleConfig.RegisterBundles(BundleTable.Bundles);

    // the nuget package does not do this for you
    AutoMapperConfig.RegisterProfiles();
}

You can then dive into the AutoMapperConfig class and tell it where to look for your AutoMapper.Profile implementations:

using AutoAutoMapper;

public static class AutoMapperConfig
{
    public static void RegisterProfiles()
    {
        AutoProfiler.RegisterProfiles(
            // put your arguments here, if you have any
        );
    }
}

As soon as you can get your app to invoke AutoAutoMapper.AutoProfiler.RegisterProfiles(), it will scan your assembly(ies) for AutoMapper.Profile implementations and automatically add them to your AutoMapper.Mapper.Configuration. See the source code for more information.

You are now free to organize your AutoMapper.Profile implementations however you see fit. What I like to do is define them in the same files as the destination types. For example:

// MyCustomViewModel.cs
public class MyCustomViewModel
{
    public string Prop1 { get; set; }
    public int Prop2 { get; set; }
}

// Also in MyCustomViewModel.cs
public class MyCustomViewModelProfile : AutoMapper.Profile
{
    protected override void Configure()
    {
        this.CreateMap<MyCustomEntity, MyCustomViewModel>()
            .ForMember(d => d.Prop2, o => o.Ignore())
        ;
    }
}

This keeps the AutoMapper configuration close to the affected type. Sometimes, you may have multiple mappings for a model. In a CQRS system, you could have an EditModel that is hydrated by an entity, but can also be converted into a Command object to send for domain processing. For cases like these, I just wrap all of the AutoMapper.Profile implementations in single static type:

public class MyCustomEditModel
{
    public string Prop1 { get; set; }
    public int Prop2 { get; set; }
}

public static class MyCustomEditModelProfiler
{
    public class EntityToModelProfile : AutoMapper.Profile
    {
        protected override void Configure()
        {
            this.CreateMap<MyCustomEntity, MyCustomEditModel();
        }
    }

    public class ModelToCommandProfile : AutoMapper.Profile
    {
        protected override void Configure()
        {
            this.CreateMap<MyCustomEditModel, MyCustomCommandDto();
        }
    }
}

AutoAutoMapper's AutoProfiler.RegisterProfiles() will still discover these implementations, even though they are nested within an enclosing class.