Project and Include.cs

static void Main(string[] args)
{
	Database.SetInitializer(new Initializer());

	Mapper.Initialize(cfg => {
		cfg.CreateMap<TrainingCourse, TrainingCourseDto>().Include<TrainingCourse, ParentTrainingCourseDto>().ForMember(d=>d.Value, o=>o.MapFrom(d=>d.Content.Count()));
		cfg.CreateMap<TrainingCourse, ParentTrainingCourseDto>();
		cfg.CreateMap<TrainingContent, TrainingContentDto>();	
	});
	Mapper.AssertConfigurationIsValid();
	
	var context = new ClientContext();
	context.TrainingCourses.ProjectTo<ParentTrainingCourseDto>().FirstOrDefault(n => n.CourseName == "Course 1").Dump();
}

class Initializer : DropCreateDatabaseAlways<ClientContext>
{
	protected override void Seed(ClientContext context)
	{
		var course = new TrainingCourse{ CourseName = "Course 1" };
		context.TrainingCourses.Add(course);
		var content = new TrainingContent{ ContentName = "Content 1", Course = course };
		context.TrainingContents.Add(content);
		content = new TrainingContent{ ContentName = "Content 2", Course = course };
		context.TrainingContents.Add(content);
		course.Content.Add(content);
	}
}

class ClientContext : DbContext
{
	public ClientContext() : base(@"Server=(localdb)\v12.0;Integrated Security=true;Initial Catalog = ClientContext;")
	{
	}

	public DbSet<TrainingCourse> TrainingCourses { get; set; }
    public DbSet<TrainingContent> TrainingContents { get; set; }
}

public class TrainingCourse
{
   public TrainingCourse()
   {
       Content = new List<TrainingContent>();
   }

   public TrainingCourse(TrainingCourse entity)
   {
       Mapper.Map(entity, this);
   }

   [Key]
   public int CourseId { get; set; }

   public string CourseName { get; set; }

   public virtual IList<TrainingContent> Content { get; set; }
}

public class TrainingContent
{
   public TrainingContent()
   {
   }

   [Key]
   public int ContentId { get; set; }

   public string ContentName { get; set; }

   public virtual TrainingCourse Course { get; set; }
}

public class TrainingCourseDto
{
   public int CourseId { get; set; }

   public string CourseName { get; set; }

   public ICollection<TrainingContentDto> Content { get; set; }
   
   public int Value { get; set; }
}

public class ParentTrainingCourseDto : TrainingCourseDto
{
   [IgnoreMap]
   public new ICollection<TrainingContentDto> Content { get; set; }
}

public class TrainingContentDto
{
   public int ContentId { get; set; }

   public string ContentName { get; set; }

   public ParentTrainingCourseDto Course { get; set; }
}