实体：

    public class Room
    {
        public Room()
        {
            this.Reservations = new HashSet<Reservation>();
        }

        public int Id { get; set; }

        public decimal Rate { get; set; }

        public int HotelId { get; set; }

        public virtual Hotel Hotel { get; set; }

        public virtual ICollection<Reservation> Reservations { get; set; }
    }

    public class Hotel
    {
        public Hotel()
        {
            this.Rooms = new HashSet<Room>();
        }

        public int Id { get; set; }

        public string Name { get; set; }

        public virtual ICollection<Room> Rooms { get; set; }
    }

    public class Reservation
    {
        public int Id { get; set; }

        public DateTime StartDate { get; set; }

        public DateTime EndDate { get; set; }

        public string ContactName { get; set; }

        public int RoomId { get; set; }

        public virtual Room Room { get; set; }
    }

  public class ExecutiveSuite : Room
  {
  }

  public class DataContext : DbContext
    {
        public DbSet<Hotel> Hotels { get; set; }

        public DbSet<Reservation> Reservations { get; set; }

        public DbSet<Room> Rooms { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Room>()
                .HasKey(r => r.Id)
                .HasRequired(r => r.Hotel)
                .WithMany(r => r.Rooms)
                .HasForeignKey(r => r.HotelId);

            modelBuilder.Entity<Hotel>()
                .HasKey(h => h.Id);

            modelBuilder.Entity<Room>()
                .HasMany(r => r.Reservations)
                .WithRequired(r => r.Room)
                .HasForeignKey(r => r.RoomId);

        }
    }

客户端代码（控制台应用程序）：

static void Main(string[] args)
        {
            // initialize and seed the database
            using (var context = new DataContext())
            {
                var hotel = new Hotel { Name = "Grand Seasons Hotel" };
                var r101 = new Room { Rate = 79.95M, Hotel = hotel };
                var es201 = new ExecutiveSuite { Rate = 179.95M, Hotel = hotel };
                var es301 = new ExecutiveSuite { Rate = 299.95M, Hotel = hotel };

                var res1 = new Reservation
                {
                    StartDate = DateTime.Parse("3/12/2010"),
                    EndDate = DateTime.Parse("3/14/2010"),
                    ContactName = "Roberta Jones",
                    Room = es301
                };
                var res2 = new Reservation
                {
                    StartDate = DateTime.Parse("1/18/2010"),
                    EndDate = DateTime.Parse("1/28/2010"),
                    ContactName = "Bill Meyers",
                    Room = es301
                };
                var res3 = new Reservation
                {
                    StartDate = DateTime.Parse("2/5/2010"),
                    EndDate = DateTime.Parse("2/6/2010"),
                    ContactName = "Robin Rosen",
                    Room = r101
                };

                es301.Reservations.Add(res1);
                es301.Reservations.Add(res2);
                r101.Reservations.Add(res3);

                hotel.Rooms.Add(r101);
                hotel.Rooms.Add(es201);
                hotel.Rooms.Add(es301);

                context.Hotels.Add(hotel);
                context.SaveChanges();
            }

            using (var context = new DataContext())
            {
                context.Configuration.LazyLoadingEnabled = false;
                // Assume we have an instance of hotel
                var hotel = context.Hotels.First();

                // Explicit loading with Load() provides opportunity to filter related data 
                // obtained from the Include() method 
                context.Entry(hotel)
                       .Collection(x => x.Rooms)
                       .Query()
                       .Include(y => y.Reservations)
                       .Where(y => y is ExecutiveSuite && y.Reservations.Any())
                       .Load();

                Console.WriteLine("Executive Suites for {0} with reservations", hotel.Name);

                foreach (var room in hotel.Rooms)
                {
                    Console.WriteLine("\nExecutive Suite {0} is {1} per night", room.Id,
                                      room.Rate.ToString("C"));
                    Console.WriteLine("Current reservations are:");
                    foreach (var res in room.Reservations.OrderBy(r => r.StartDate))
                    {
                        Console.WriteLine("\t{0} thru {1} ({2})", res.StartDate.ToShortDateString(),
                                          res.EndDate.ToShortDateString(), res.ContactName);
                    }
                }
            }

            Console.WriteLine("Press <enter> to continue...");
            Console.ReadLine();
        }



using ( var context = new DataContext() )
{

        //context.Configuration.LazyLoadingEnabled = false;

        // Assume we have an instance of hotel
        var hotel = context.Hotels.First();
        var rooms = context.Rooms.Include( r => r.Reservations ).Where( r => r is ExecutiveSuite && r.Reservations.Any() ).Where( r => r.Hotel.Id == hotel.Id );
        Console.WriteLine( "Executive Suites for {0} with reservations", hotel.Name );

        foreach ( var room in hotel.Rooms )
        {
           Console.WriteLine( "\nExecutive Suite {0} is {1} per night", room.Id,
                             room.Rate.ToString( "C" ) );
           Console.WriteLine( "Current reservations are:" );
           foreach ( var res in room.Reservations.OrderBy( r => r.StartDate ) )
           {
              Console.WriteLine( "\t{0} thru {1} ({2})", res.StartDate.ToShortDateString(),
                                res.EndDate.ToShortDateString(), res.ContactName );
           }
        }
     }

我尝试投影并将其放在匿名对象中：

       var hotel = context.Hotels.Select(h =>
        new 
        {   
            Id = h.Id,
            Name = h.Name,
            Rooms = h.Rooms.Where(r => r.Reservations is ExecutiveSuite && r.Reservations.Any())
        }).First();

但我得到一个例外：“ DbIsOfExpression需要一个表达式参数，该表达式参数具有与该类型参数兼容的多态结果类型。”

现在，如果您会注意到，我以两种不同的方式实现了它，首先是通过显式加载相关实体，其次是通过进行两个不同的查询，我的问题是，有没有办法可以加载对象图并过滤对象我从数据库中进行一次旅行就“包含”了哪些实体？