渴望在 LINQ to SQL 中加载子列表

Question

我正在尝试优化 LINQ to SQL 请求，以使其生成单个 SQL 语句。目前我有这样的事情：

EDIT ：为清楚起见删除了“where”过滤器 - “Id” 也是两种对象类型的数据库中的主键

hotel = (from h in db.Hotels

         let rooms = (from r in db.HotelRooms
                      where r.HotelId == h.Id
                      select new HotelRoom
                      {
                          Id = r.Id,
                          Code = r.Code,
                          Category = r.Category
                      })

         select new Hotel
         {
             Id = h.Id,
             Name = h.Name,
             Rooms = rooms.ToList()
         }).FirstOrDefault();

酒店业务级别类定义为：

public class Hotel
{
    public int Id { get; set; }
    public string Name { get; set; }
    public List<HotelRoom> Rooms { get; set; }
}

其中查询使用初始化程序在执行查询时从 DataContext 实体动态创建 business 对象。

问题显然是，Rooms 集合上的 .ToList() 会导致通过第二个查询填充 Hotel.Rooms 集合。

有没有办法用所有 HotelRooms 填充 Hotel.Rooms 属性，而不会产生额外的查询？

Answer 1

  //grab the rows from the database in direct fashion.
var joinedRows = 
(
  from h in db.Hotels
  where h.Name == name
  from hr in h.HotelRooms
  select new {HotelRow = h, HotelRoomRow = hr}
)
.ToList();

  //shape the data locally
List<Hotel> result =
  from row in joinedRows
  group row.HotelRoomRow by row.HotelRow into g
  let h = g.Key
  select new Hotel()
  {
    Id = h.Id,
    Name = h.Name,
    Rooms = (
      from r in g
      select new HotelRoom()
      {
        Id = r.Id,
        Code = r.Code,
        Category = r.Category
      }).ToList()
  };