Question

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

编辑：为了清晰起见，删除了“where”过滤器 - 同样“Id”是两个对象类型的databsse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; }
}

其中查询使用初始值设定项在执行查询时从DataContext实体动态创建 business 对象。

问题是，很明显，Rooms集合上的.ToList()会导致通过第二个查询填充Hotel.Rooms集合。

有没有办法用所有的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()
  };

急于在LINQ to SQL中加载子列表

1 个答案: